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I'm charging a flat battery with a mains charger. I'm curious if the mains charger can also be used to jump start... If it delivers enough power?

The instructions make no mention of this at all, did that mean even if it won't work, there's no safety concern?

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Presuming it's a standard "trickle" type battery charger and not a "jump pack", I wouldn't advise attempting to start a vehicle with the charger plugged in. The typical result, with a flat battery, is that the vehicle attempts to draw the power required to turn the engine over (the biggest ever demand on a car battery) from the low output charger and overloads the charger.

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  • It's some sort of "smart charger" but not a jump pack. It claims to be rated up to 9A... I have no idea what load starting the engine puts on the battery for comparison!
    – Mr. Boy
    Commented Aug 21, 2017 at 13:02
  • 400 AMPS is sufficient to start most cars. mechanics.stackexchange.com/questions/18329/…
    – Steve Matthews
    Commented Aug 21, 2017 at 13:05
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    I can attest to Steve's advice above. He told me not to do this. I didn't listen and tried to start my care when the battery was being trickle charged. The end result: the care didn't start and I blew two fuses in the charger.
    – Jamie Leishman
    Commented Aug 21, 2017 at 13:16
  • FWIW most chargers I've used have a built in circuit breaker that will automatically reset in this situation. So you aren't really hurting anything. Not that the extra 10 amps is going to do much to help start the engine either.
    – agentp
    Commented Aug 22, 2017 at 11:44
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You may be able to... if the battery is at full charge.

Best not try it. A battery charger delivers a few amperes at most. A properly charged battery delivers enough to turn over a starter motor or to melt a steel bar put between the poles.

(Hint: do not drop steel tools on both the + and - poles. If you are curious google on it instead).

The result is akin to a bucket of water slowly being filled from an outlet. The water bucket can deliver a lot of water in a short period. The outlet slowly fill it. If you try to drain a lot (water|amps) from the outlet then it will either blow a protective fuse or it will burn out.


Note that there is a distinction betweeen jump starters and regular chargers. I assume that with charger you either meant a regular charger or a trickle charger and not a jump starter.

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