How should I recharge a 7.4V battery?

I have a 7.4V rechargeable battery and I'm wondering what voltage I should be charging it with.
would 9V work?
Are there any general guidelines for recharging batteries?

1400 mAh
Was originally used in a NXT LEGO robot.


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It is generally considered a bad idea to try to charge lithium batteries without the proper charger or a voltage/current limited power supply. If you get it wrong, lithium batteries are likely to be damaged, catch fire or in some cases explode.

If the original application is still able to charge the batteries, that is the best option. Otherwise, you should build or buy a suitable charger. While you are trying to charge them you should monitor the temperature to try to avoid any serious issues.
jensenr30 (author)  The Skinnerz5 years ago
thanks for the advice! I'm going to look up how to make battery chargers.
I'm guessing I'll want a resistor to limit the current.

VenkyT2 years ago

From personal exp.

check this thing important : 1.voltage (v) 2. current (amps)

ex: 12v 1 amp dc battery will bulge / explode when charged with 12v 10amp dc supply.

I supplied my 12v 1amp battery with 12v 15amp supply and made them look like big muscle men, after three hours of charging. ( they still work ) due to the above stated ignorance.

so consider checking your battery current in amps to avoid explosion.

if you need to explode a 12v 1amp battery - do this (don't do) :

connect the battery to a dc power supply with 30amps+ current and let it charge for 1 hour(s) or less...


Make sure you find instructions for a Li-Po battery charger at the correct voltage, as attempting to use a charger designed for other battery types can be dangerous.
jensenr30 (author)  The Skinnerz5 years ago
Good point. I have measured my AA battery charger and it outputs roughly 3V.
Needless to say, this is not the right charger for the job.
No! Make sure the battery charger you are using is rated for Lithium ion (or li-ion). Just a plain old charger, while might work, could blow up your battery. I think you can buy chargers on ebay rated for a 7.4v for pretty cheap if you have $10 or so
jensenr30 (author)  astroboy9075 years ago
I said "this is not the right charger for the job." As in, I wasn't going to use it. did you just misread it or am I misunderstanding you?
Just emphasizing ;)
pfred25 years ago
Whatever happens post an article here and share your adventures with us! It looks to me like you already have one image.
jensenr30 (author)  pfred25 years ago
i will