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Can you charge a car battery with a portable power generator?

Say you have a lithium, not petrol, generator, something like this or this, which you can charge in the electrical socket at home. If you then connect the vehicle battery to a battery charger (like an Optimate, Ctek, Noco, etc) and plug the charger into the generator, would that work? Is there any reason why it wouldn't be recommended?

Of course if you have your own garage or driveway there's no need - but not everyone does.

Can these things be left unattended? E.g. if you have a garage without a plug. Or would it be a safety hazard? Modern chargers are meant to be left on and unattended for prolonged periods of time, but I have no idea about portable generators.

Would it be dangerous to leave the generator in the car, e.g. on a seat, leave the windows slightly open but lock the car? Lithium generators don't create fumes.

PS Some portable power generators have a 12V output but I imagine that charging a vehicle battery with a dedicated charger is better than directly from the 12V output

PPS What kind of specs would one need to check? Maximum amperage? Is there any particular risk from leaving these "big batteries" in the car while charging the car battery? Maybe if the car is under the sun and the inside gets too hot that could be a hazard?

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    Those are not generators but big batteries and will run down at some point, but yes you can do it. – Moab Apr 23 at 1:52
  • There are lithium packs specifically designed to charge a car battery. – Agent_L Apr 27 at 15:38
  • Can you please show some examples? So far I have found the PowerOak lithium battery packs on Amazon, which are very generic. Also, what capacity would I need? If a charger takes about 12 hours to charge a car battery at 12V 4A, then should I be looking for a capacity of ca. 12 * 12 * 4 = 576Wh? – Pythonista anonymous Apr 27 at 15:43
  • @Pythonistaanonymous Add * 2 for conversion loses, so closer to 1kWh. Also, the lead-acid charger usually switches to trickle mode when full, so if you leave it long enough, it'll drain the li-ion pack down to zero, so don't expect more than 1 charge. – Agent_L Apr 27 at 15:49
  • 1 Kwh packs are too big. Maybe a 500Wh pack to be used in two steps? Or maybe just once - after all, I shouldn't recharge the battery from flat but before it gets there, so it shouldn't take 12 hours. – Pythonista anonymous Apr 27 at 15:52
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Yes, generally you should be able to use any 120V equipment on the portable generator, provided you don't go above the maximum power rating.

So yes, you can plug a battery charger.

As far as leaving the generator in the sun, it should be specified in the operating manual.

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Whenever they can be left unsupervised is stated in their manual. Both the big lithium pack and the wall charger can have "do not leave unsupervised" clause and you should respect that.

Lithium batteries have a nasty tendency to catch fire for the slightest reason. Like overcharge, undercharge, overcurrent, overheat, etc. So, a failure of the control circuit in the pack can turn it into flamethrower, and a big pack will throw really big flame. This is rather extreme scenario, but will you risk your car? If the car is not shielded from sun, the just leaving the pack on the seat can be dangerous.

12V pack can't be used to charge the car battery directly, you'll need a charger with 12V input rather than a common 110 or 220V one.

But - have you considered simply buying another car battery and using one in the car while charging the other at home, then swapping? Should be way cheaper than 1kWh lithium pack. Cheaper and safer, but heavier.

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