Charging 12V Batteries With A Generator

Charging 12V Batteries With A Generator:

You’ve bought a camping inverter generator with built-in 12-volt outlets. But how do you go about charging 12V batteries from your generator? Here’s a quick rundown of what you need to know.

The Yamaha EF2000iS inverter generator control panel with DC outlet at the bottom

Let’s get straight to point: camping generators may have a 12-volt output on them, but when it comes to the crunch, they are not designed to fully charge your batteries directly. There are two main reasons why:

First, the chances are your generator’s DC outlet is limited to a current of about 8 amps maximum. So any battery will take a while to fully charge.

Secondly, the voltage of the DC output isn’t regulated – it varies according to the generator’s RPM. This is fine if the generator is running a low load, but not if it’s running a medium to high load. Also, the generator won’t cut back the charge when the battery is nearly full, so you can’t risk leaving it charging for too long.

The bottom line: Your DC output on your generator is best for emergency or short term charging, i.e. providing your car battery a trickle charge. Anything more is a potential risk to your batteries.

The DC outlets on an inverter generator are good for small trickle charge to re-start a car battery
So What’s the Solution?

The best way to charge your battery is to run a proper 240-volt battery charger off the generator’s AC output. This will recharge the battery much faster and accurately. Also, most chargers regulate themselves down, so as charge builds in the battery, the charger won’t be pushing the same amount of amps.

So as a backup or alternative to your solar set up to charge your camping/caravan/motorhome battery packs, portable inverter generators are a great option, especially as you can also run your appliances on 240v straight from the generator also. But just remember, when charging your battery packs off a generator, use a quality battery charger plugged into your 240v outlets instead of the generator’s DC outlets.

You can read more about battery chargers in our “Battery Chargers for 4×4, Off-Road and Camping” blog. You can also watch the below video from our friends at Enerdrive (who make excellent AC to DC Battery Chargers for hard wired installations) demonstrating their ePower chargers:

Enerdrive eTips – Enerdrive ePower Battery Chargers

If you’re looking for a plug & play option, you can simply plug a good quality smart charger into the AC outlet of the generator and connect the 12V charging cables to the positive and negative terminals of the battery. Try to find a battery charger that comes complete with the charging cables, for example the Victron Blue IP65 Smart Charger 12/15 + DC connector.

For a full range of quality battery chargers, check out our site HERE which includes options from leading brands such as Enerdrive, Victron, C-Tek, Projecta, BMPRO and more.

For camping inverter generators, check out the expert selections or explore the full range at My Generator. The most popular model for charging your camping battery packs (via a battery charger) is the Yamaha 2200w Inverter Generator Pack. This model while remaining lightweight and compact, still has enough power to run rooftop air conditioners and other appliances in your caravan.

Yamaha EF2200iS – The perfect balance between power & portability


Shop our full range of Inverter Generators here!

DISCLAIMER* Please note, this advice is general in nature and we strongly recommend consulting the product manual and where relevant, a professional installer.

Sean Connolly

Sean is the co-founder and Director of My Generator (mygenerator.com.au) with a keen in interest in the outdoors and power products.

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70 thoughts on “Charging 12V Batteries With A Generator”

  1. Hi Sean I’d like a generator to run a small coffee machine in my Chrysler 300c stretch limo. Coffee machine is Nespresso pod.
    Wait for your response, Steven.

    1. Hi Steven,

      Thanks for your inquiry. We have helped many customers with selecting the right generator to run their coffee machines. The first and most important thing you need to do is to find out the starting and running wattage requirements of your machine (the starting wattage for some coffee machines can be quite high). This wattage information can be found in the product manual, on the product data plate, or you can contact the manufacturer to ask them. Make sure you get the starting wattage (this is the most important) as sometimes the specs will only list the running (or rated) wattage.

      Once you have that starting and running wattage info, you can then choose a generator which will be able to power your nespresso machine. You can check out our range of inverter generators (which would be the most suitable type for your purpose) and sort by Power Output to find the right sized generator model for you.

      You may like to talk to an expert if you have any more queries, in which case please call us on 1300 400 122. Many thanks!

    1. Hi Avinash, we are not aware of a portable generator on the market that just produces DC power. However most inverter generators available today have DC outlets as a secondary power source to the AC outlets. With DC cables you can provide a trickle charge to car batteries to get you going. However it is not recommended that you fully charge your battery from the DC outlet, as the power is not regulated. Its only advised that you provide a small trickle enough to kick the car over. To fully charge your batteries using a generator, it is recommended you use the AC outlets and connect a battery charger between the generator and the batteries – this will properly regulate the power. Thanks

      1. Is it possible to hook up the 12v DC outlet to a solar charge controller then connect that to the battery to charge ?

        1. You Sir are a genius….. great idea and I can’t see why it wouldn’t work.
          I have a small generator with 12 volt output and wondered how it was to be practical if not regulated.
          Most solar controllers will accept up to 24 volts so should be able to handle any spikes…..
          Let me know if you have put it to a test and what was the outcome.

  2. Interesting you talk about using a 240 VAC charger as most people would have a 120 VAC charger, but either works and all generators have 120 VAC. Just and observation, but your comments are right on about charging. charger vs. 12 VAC.

    However, in the event I have to charge from a generators 12 VDC system, (Honda 1000) what wires do I need? How heavy (gage) would I need to get max current to the battery? I am looking at this as an emergence charge / boost to get something started. Suggestions?

    1. Hi Steve – great point, we will amend the post. It should read ‘240 Volt and 120 Volt chargers’.
      In terms of wires for your Honda 1000, we would advise you opt for a Honda 12Volt DC Charging Lead – for Honda Generators, these need to be purchased separately.
      Hope that helps, cheers.

    2. As usual an American who thinks they are the only people in the world. It’s an AUSTRALIAN website and in Australia we use 240 volts.

  3. Hi Sean
    I play my music in my camper van for several hours and often run my battery down. Would it be ok to power my 6 amp trickle charger from my honda EX650 generator onto my vans 12 volt battery while I am playing music with the ignition off?

  4. I recently bought a Gentrax 3.2KVA generator for the purpose of doing odd jobs on my block of land.

    I was wondering, is it possible to connect a 12v Deep Cycle Battery to some part of the Inverter side during the evening when no one wants to hear my generator chugging away to produce 240VAC?

    Alternatively, I would need a separate Inverter.

    Any Ideas??

    1. Hi Mark, from my understanding of what you are saying, you would need a separate inverter for this. The inverter within the generator could not act as the channel between your battery and your AC appliances. Thanks, Steve.

    2. Best to buy a proper inverter and not try to feed the internal inverter of a inverter generator. Circuit protections and overload protections are different. In the case of the inverter board installed in the generator it would not incorporate reverse polarity or over/under input voltages which stand alone inverters have as standard. Also there may not be input output isolation of the battery and 240 volt output leading to a possible shock hazard. Stand alone pure sine wave inverters of about the same output as the Gentrax 3.2 kva are only about the $300 mark, Make a mistake with the Gentrax inverter module and that would cost about $600 to replace

  5. I have a 3.6KVA inverter connected to four 150AH batteries with a charging current set at 12A. This inverter is connected to normal load.

    At the depletion of inverter power and in the absence of normal power, if I want to run the normal load off the generator, and any remaining current off the generator to charge the batteries connected to the inverter, is it possible?

    In other words, if I connect a 4KVA generator to charge the inverter batteries while 2KW is being used by the normal load, would the generator shutdown because of overload or would the inverter slow down its charging to run the normal load? The other way to ask the same question is, would a 4KVA generator suffice or would I need a higher rated generator?

    1. Hi Viki, it would all depend on your battery charger, your batteries and how much power they would draw. Typically for standard camping battery packs / normal vehicle auxiliary batteries, charging them through a regulated battery charger will not draw much power at all.
      You need to know the running (continuous) watts of your generator, and if you are drawing roughly 2000 watts from other AC appliances then the difference between those two is the capacity you have to charge your batteries without overloading your generator. Hope that helps – cheers, Steve.

    1. Hi Bill, to run 12volt appliances it’s advised that you use the AC output of the generator and then an inverter. The DC output of a generator provides unregulated power and is really designed for small trickle charge (say a flat car battery) purposes if required. Hope that helps – thanks, Steve

  6. Hi Steve,
    We’re about to embark on a trip through the Simpson desert and up to the Gulf Country, if it becomes dry enough by mid to late April.

    We’ve got a slide-on camper with an old 80 Litre Everkool fridge, which we will want to use as half freezer, half fridge. Other electrical use is minimal, apart from a CPAP machine, which draws 2 Amps, when being used.

    I anticipate wanting to spend up to 4 or 5 days in one spot, without shifting camp, meaning that the 115 Ah auxiliary battery won’t last, without charging. In fact, at the moment, I’ve two auxiliary batteries in series (100 Ah & 115 Ah), but I’m seriously thinking of substituting the smaller battery, by buying a Yamaha 1000 iS generator as a back up. This will save about 10 kgs in weight and provide me with the power security I want.

    The camper is rigged with two CTek chargers, namely one 240V Multi XS 15 Amp charger, for powered sites, and a Dual 250S DC-DC charger for recharging via the car’s alternator. I note your earlier comments about the DC supply being unregulated, but won’t this be overcome by the DC-DC charger regulating the charge?

    My main questin is, what mode would be quicker/more efficient to recharge the battery, a) using the 240V power lead into the external socket on the Camper, or b) running the DC lead into the input side of the DC-DC charger?

    If using the 240V 20 metre long orange extension lead to recharge the battery from the generator, will it pay to suspend the lead 30 cm above the ground, to minimise loss due to induction?

    Regards, Alan.

    1. Hi Alan, great questions. The Yamaha EF1000iS is very popular for your type of application. In our experience, using a good quality 240V charger is a very safe, quick and effective way to charge your batteries. I’m not as familiar with DC to DC charger unfortunately, as I don’t have one – all I know is that the DC outlet on inverter generators do not provide a regulated charge. However, if you are confident that your DC to DC charger correctly regulates the charge (which it should), then it would most likely be fine.
      In terms of extensions leads, any generator’s capacity can be diminished by the length and quality of the extension chord – our tests suggests that anything over 3-4 metres in length can start to slightly de-rate the generator’s power delivery. The power loss is not significant, but the longer the chord, the more it can de-rate.
      Hope that helps, cheers – Steve

    2. Hi Steve,
      I’m back again, after completing my trip across the Simpson and up to Lawn Hill.
      I was surprised how long it took to recharge the two 100 AH lead acid batteries, using the Yamaha EF 1000iS generator.
      The extension cord was a typical 20 metre long 15 Amp orange cord, which I’m thinking has fairly thick insulation. With the generator producing 800 Watts, or 66 Amps at 12 Volts, I’m presuming there is ample current to overcome any induction loss?
      The battery charger was a CTek 15000 (15 Amp), converting the 240V output from the generator. I’m guessing that I could expect 60 Amps to be replaced in the batteries in four hours, if there is 100% efficiency and that 45 Amps in four hours could be more realistic.
      I’m seeking your advice on using a CTek 25000 model to speed up the charging, instead of the CTek 15000.
      If I do this, will it be too rapid a charging rate, if I use this 25 Amp charger on a single 120 Amp Hour AGM battery, which is what I use in the other light weight 4WD car we have?
      I have heard it is better to stop recharging, when the battery is 80% recharged, because the last 20% takes almost as long again; a bit like pumping up a bicycle tyre by hand.
      So I’m not looking for a full recharge, just enough to bring a healthy amount back into the auxiliary batteries, for the next day’s draw.
      Alan Pickering

  7. why cant the dc output be used to power a dc light that can use dc power from 12v to 32 volt dc amp draw is very small as it is led bulbs

  8. Sean; I purchased a Champion 3100 Inverter Generator. It works well and I’m happy with it. I’m aware of using a digital battery charger plugged into one of the AC outlets to charge batteries…but. I would like to take advantage of the 12V / 8a outlet (waste not, want not!). Seems to me I could route that 12v output to a good MPPT Charge Controller attached to my travel trailer’s battery system to charge the batteries. Your thoughts on this would be appreciated before I purchase a pricey MPPT unit. John

    1. Hi John,
      As you have rightly indicated, we recommended using the AC outlet via a quality battery charger to recharge your batteries. In terms of the DC outlet, we only recommend this for emergency battery charging, i.e car breakdown.
      My understanding of an MPPT controller is that it is used for Solar power set ups to convert the excess voltage from your solar panels into amperage to top up your batteries. You will need to contact the manufacturer of your generator and battery to check if this application of an MPPT controller is suitable.
      Regards, Steve

  9. Hi, in terms of battery charging; provided I am using an AC outlet with a quality battery charger, do I need to disconnect my main car Battery before charging it with an inverter generator like the Yamaha 2400?

    1. Hi there, Thanks for the question. You do not need to disconnect your main car battery in order to recharge. The Yamaha 2400 will be more than adequate to perform this operation. Good work on choosing a quality charger, just be sure to “always” read the battery charger’s instruction manual prior to use.

  10. Hi, I have 2 x 100ah batteries in the Complete Campsite camper trailer that currently supply a Waeco CFX50 fridge, some 12v LED strip lighting and the occasional use of a 12v pump for water from tank to kitchen. (Some 12v phone/tablet charging may also be on the cards during the stay) We are planning a 10 day camping trip earl next year at an unpowered site, with the use of an 80w Sunpower solar panel to keep us going. Question is, I’m thinking of taking a GMC generator that the father in law gave me for additional power backup. Will this put out safe power to supply the 240v battery charger for the batteries or do I need to do/add something else to allow us to utilise the generator to charge the batteries whilst camping?

    1. Hi Ben, I would recommend you check you battery charger requirements in terms of the type of power supply required. Typically for camping applications, inverter generators (with pure sine wave power) are used. However, we supply conventional generators for all manner of battery charging (including solar systems) without issue. Again, you are best to check your charger to see if there are any specific power supply requirements. Thanks.

  11. My Application has a 72V 100AH Battery Bank. I am interested in Just charging the Battery Bank While I am at Rest stops. Possibly at Night when I am Sleeping. Therefore I would like to know if This Generator Can Charge my whole battery bank with On Fill Up? My application has a Onboard charger to Regulate The Power being sent to the Battery Bank. I am interested in Saving Weight and Efficiency. If A 1000watt Gen can do the job in 8hrs or so I am satisfied with that.

  12. What type and specs of dc generator is required for charging a car battery? Car weighing about 170kg .. I need to give power to a dc motor to run the wheels? Generating electricity through mechanical system and also using a diode circuit to control the dischrging system of the battery? can you help?

    1. Hi Waqar, most of the DC power sources on inverter generators are designed for a brief trickle charge as a backup, not for continuous running power as it is not regulated. Thanks

  13. I have a 72v 100Ah battery pack with a 30amp charger. Can I charge the battery pack at 400 watt = 1/4 load and be able to charge the whole battery with one Gallon on a 2000w Gen?

  14. I want to charge 12v, 48v batteries from bldc generator inbuilt in electric bike.
    Other than using transformer, which is the suitable method for charging the batteries?

  15. Hi,
    I would like to run a 200W 12v motor on an olive picking machine and wonder if there it can be run off the 12v outlet on a genrator rather than having to us a battery?
    If not, what size battery should I be looking for?

    1. Thanks very much for the question Mark.

      Your olive picking machine will draw approximately 17Amps /’ Hr.

      The 12 Volt Outlet on the generator will not be powerful enough to provide this much amperage. The 12V outlet on the generator is designed for battery trickle charging only.

      You will need a 12V power supply that produces greater than 200W and can be plugged into the AC outlet of a small inverter generator like a Yamaha 1000W inverter generator

      These products draw about 600W AC, are readily available and range from $150 – $300.

      Feel free to call 1300 400 122 to speak to one of our product experts about this application.



  16. Thanks Paul,
    I rang and spoke to someone but he said you don’t carry any transformers with enough grunt for the motor with the ones you have for fridges only going up to 150W. I have seen transformers in Bunnings that are rated up to 400W for outdoor lighting. Would you foresee any issues using one of these? I would imagine it doesn’t matter what the power is used for, just that there is enough? Same as plugging in a lamp into a power point as opposed to a large plasma screen TV?

    1. Hi Mark,

      Yes, this will be suitable for your application. As long as the transformer produces enough wattage to power your appliance you will be fine.



  17. Hello Folks,
    I wish to run a 1kva inverter generator, not any larger or noisier than that, to power a 12v or 24v proper battery charger. How can I determine the highest wattage charger I should attempt to power?
    Your Enerdrive 60a 12v (720w) unit can be ‘dialled back’ to suit a 1kva generator – this implies a limit between 480w and 720w.
    Important consideration!
    Thanks, Kurt

      1. Hi Paul,
        Can that maximum draw of a battery charger be roughly predicted, like this?
        ChargerWattage / (Efficiency x PowerFactor): say… 720 / (.79 x .87) ~= 1050
        Or more likely:
        (ChargerAmps x ChargingVolts) / (Efficiency x PowerFactor): say… (60 x 14.4) / (.92 x .90) ~= 1050
        If so, matching a charger to a generator becomes less risky.
        The dial-down feature of that Enerdrive charger is an asset, especially if mains power is sometimes available.
        Cheers, Kurt

  18. Hi,what size generator would i need to charge a 100ah deep cycle battery ?I have 180w solar panels which do the job but in the advent of bad weather i would like to use a generator with 240v battery charger .Thank you

    1. Hi Norman, it is important to match the battery charger to the generator. Most battery chargers will draw less than 900W, therefore we would recommend a Yamaha EF1000iS inverer generator, which is the most popular model for purely charging camping/RV batteries – it is very light at 13 kilograms and super quiet. If you need a bit more power, then you would consider the slightly larger Yamaha EF2000iS generator model, which is also a very popular recreational generator. Many thanks.

  19. I have a 36v onboard charging system in my bass boat. I don’t have shore power. I want to get a real quiet inverter type generator to run this charger from the 120v inverter output. Can someone tell me what size inverter I will need?

  20. Hi there I am looking to buy a generator to charge two 110 AH deep cycle batteries in my caravan. I have a BM Pro Battery Plus 35 Battery Management system in my van.
    I tried using a Honda 1000w generator to charge through the 240 volt outlet but it kept overloading, how can I tell if a 2000w machine will do the job for me. I don’t want to buy it and find it does not work

  21. hi, so what is stopping you connecting a small petrol engine [like lawn mower /chainsaw] to a 12volt alternator and feed your batteries direct from the alternator ,i am really interested in this as i want to power my pushtrike this way

  22. Hi, I have a cheaper 2000 watt generator (link below) that has both the AC and DC outlet. I’m pretty sure the inverter on the generator for the AC is not a pure sine wave like some of the more expensive generators. Do I need a pure sine wave generator for the battery chargers that you are recommending to charge a 12 volt deep cycle?


  23. I have a Noco onboard charger in my ice house. 10 Amp. When I plug into wall , it works like a champ. I just got a 2000 watt investor generator and it will not power the charger. The investor powers my air compressor, table saw and any hint else I plug into it, but will not power the charger. I am at a loss here

    1. Hi Bruce,

      I’m not really sure what the issue could be. But it’s worth checking the following things.

      What is the max power draw of your battery charger? It needs to be under 2000W.

      Some switch mode chargers like yours require pure sine wave power. Does your generator produce pure sine wave power?

      You could try starting the generator first and then turning on the charger. The generator may need to get up to speed first.

      Let me know how you go


  24. In practical terms you won’t gain more power by using the AC. The rms dc equivalent is about 10 amps. The charger itself would likely consume a couple of amps.

    It’s true the charger would regulate the charging to proper levels and should be used for those reasons.

  25. I have a Yamaha EF2000iS generator. What size/type battery charger would I need to connect to the AC point on my generator to power up battery to use for lighting, fridge etc.?

    1. Hi Karl,

      You can use a wide range of charger sizes to do this. The battery charger will be rated in output. For example a 20A charger will put out a max of 20A into your battery. The bigger the charger the quicker you can charge your batteries.

      The battery charger will also have a max input rating. You want to keep the max input rating below 1600W for the EF2000iS or about 6Amps. Be sure to check the max input rating before selecting your charger.

      This CTEK MXS 25 12V 25A Battery Charger will draw approximately 700W at full charge. So it would be ideal to use as a battery charger with the EF2000IS

      Feel free to call me on 1300 400 122 for more charger options and information



  26. Hello,

    We’re learning to live on a sailboat and are building up our power charging capacity. Am a bit stumped why all of a sudden today, while running our panda generator our inverter/charger is shutting itself off. That never happened previously, thus a bit stumped. Can you suggest anything?

  27. Question about hookups.

    I have 2 batteries wired in parallel on my travel trailer. I also have the yamaha 2000 generator pictured in your post. Also have a battery charger with 2 sets of alligator clips that I use to keep batteries charged in the winter.

    How do I hook up the setup when boon docking?

    run generator
    plug in charger to generator
    ?? plug one set of alligators to the first battery?… plug both sets onto each battery?


  28. Im using a 6500 generator to charge my battery bank of 8 batteries that are essentially 2 24 v by the way they are wired together in pairs. I have an inverter and other sources of power from solar and water power. in the off seasons, i must use a generator. I’m wondering if I could go down to a smaller generator to save gas if I’m only charging my battery bank..Any ideas? There is an inverter involved in my system ..

  29. I have a dodge ram 2500 truck. Want to install 2000 watt running / 4000 watt peak inverter with extra 12 volt deep cycle battery to use in evening so I don’t have to run loud generator. Was told I couldn’t do that because I would only have power for a few minutes and my vehicle couldn’t recharge the extra battery next day unless I drove 300 miles … I do have a Ryobi 2300 generator but don’t want to use it at night time. Any ideas of what I can do?

  30. Hi Sean,

    I have a solar set up with 6 110Ah batteries (12v 600Ah) and need a back up charger, I need a generator with enough output to run a battery charger, what would you suggest??

  31. I have honda lt7000ec generator with two plugs one for the ac and other for the dc the rated current is 5.0 kw or it might damage the car battery?? i am asking can i charge my car battery with it if its flat or it might damage it or it isn’t suitable at the first place

    1. Hi Essam – a trickle charge from your generator for a short period will be fine. Typically the DC charge from a generator is not designed to fully charge your battery though – just enough to get it going if your car battery is dead. To fully charge your battery, you should look at using an AC to DC charger from your generator which will properly regulate the power.

  32. Hi,
    I have a EF2000IS and it has killed me battery charger !!?
    I bought a battery charger to handle two 100ah lead acid deep cycle battery’s and charged them
    at home with no problems when at our camp spot it and decided to boot the batteries a bit
    I started the generator plugged in the battery to the charger then to the generator and it went pop.

    Any ideas why this would have happened the only other thing running was a 150 watt led light extension lead and double adapter ( the charger was a MCU070 )

    1. Hi James,

      Sometimes if a generator does not produces clean power and the frequency is out, it can damage chargers. But the Yamaha produces pure sine wave power at 50Hz sop this should not be a problem.

      You may have to contact the manufacturer of the charger to see if they can shed some light on the issue. I tried to research your charger, but could not find any specifications online. Do you know the peak power draw of one of those chargers?



    1. Hi Geoff,

      We don’t sell the Jackery 500, but after a quick search on the Jackery website, it does come with an AC charger so you should be okay to plug that into your generator to recharge it. We would recommend using a good quality pure sine wave inverter generator to ensure that the power is a clean input. If you don’t have a generator, you can shop our range of pure sine wave inverter generators here: https://www.mygenerator.com.au/inverter-generators.html


  33. Hi I have found this page while looking for a trickle charge option for my garage that has no power.

    My plan would be to plug a ctek mxs 5.0 into a power station and then leave it topping up the battery but I am told it would be inefficient. I do kot understand calculations enough to work out runtime and also belive that once the Ctek hits the float mode it would last alot longer than on the charging part which on the car battery would be minimal as would be plugged in once parked up.

    So I can reference run times what runtime would you expect from the yamaha 2000w power station you reference above powering a ctek on a 12v car battery?


    1. Hi Joe,

      By “Yamaha 2000W Power Station” I assume you are referring to a Yamaha 2000W Inverter Generator?

      If you only have a Ctek mxs 5.0 battery charger connected to that generator, the generator will perform maximum run time.

      You are correct, that the Ctek charger will consume less power in float mode, but the calculation is redundant for your application. The difference in power consumption is negligible.

      The Ctek charger will draw about 325 watts from the generator. 324Watts is below 1/4 load of the continuous power output.

      Yamaha advertise a run time of 10.5Hrs at 1/4 load on a full tank of fuel.

      I would expect a similar run time for your application.

      Kind regards,


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