Author Options:

How can I recharge 3.7v Li-ion batteries from cellphones... if I have 3 of them attached in a serial array? Answered

I'm trying to turn a cheap pc-speaker set into a battery operated set. I have a lot of 3.7 Li-ion batteries from dead cellphones and I want to solder them into a serial arrange to get 11.1v. The question is... how to recharge them? is it safe to recharge with a 12v dc adapter? any other idea?

Thank you!


The forums are retiring in 2021 and are now closed for new topics and comments.

Answer 11 years ago

EXCELLENT video. This needs to be put prominently on Instructables; makers need to properly understand the risks they're taking.

High-energy batteries (Lithium or NiMH) are NOT A TOY. Chargers in particular need to be carefully designed or you can get literally explosive results. Treat these the way you would treat lighter fluid, which can also be explosive under the wrong circumstances. You don't have to be completely paranoid -- but if you do not know what you're doing, you can do serious damage to your surroundings and/or yourself.


11 years ago

As Re-design says, they're fussy buggers as the video shows.

They need to be constant current charged at 1C (i.e. the ampere hour rating of the battery) until the terminal voltage of has risen to 4.2V and then constant voltage charged until the current drops to below 3% of the original.
Don't try trickle charging as that can do Bad Things to them.
Also, they shouldn't be discharged to below 2.7V or it can make the cell dangerous.  Most equipment will have a safety cut-off at 3V or so.

I've designed a PicAxe controlled charger for charging cells to the spec, but I haven't had time to build it yet.  Testing will be done very tentatively.