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Cheap Lithium ion batteries - help? Answered

I picked up 4 Canon NB-4L batteries for 50p each, thinking that for the price they might be worth having.
However, I don't have a charger - any help with this?
I've got power and electronics and stuff.
3.7V 760mAh (Li-ion)


Oh yes, I'd want to measure what the thing was doing. But I was hoping for a schematic...


Kiteman was on to something.
If they're the same voltage and material as a cell phone battery, you could hook up wires from the cell phone battery contacts to the battery terminals. Make sure the phone's 3 contacts are used with the battery's 3 terminals correctly. Your normal cell phone battery should be analogous to these batteries in the terminals (voltage, GND, voltage). That should help indicate where to connect. Your phone will view it as a different battery and charge it using its smart circuits.
If the contacts are recessed (like mine were when I did this), put small bits of aluminum foil in the recesses and tape wire leads to that.

It is probably advisable to use an old cell phone instead of your nice new one, just in case of some catastrophic FAILure.

OK, that helps a bit, thanks.


Li-Ion batteries take a two stage charging technique where the rated charge current is applied until the voltage gets to a set level (usually about 4.2V), then that voltage is held until the current drops to ~3% (~10% for LiPo) of the rated charge current.

This shouldn't be too hard to rig up, but if there's a bug in the system things could be pretty bad.

It's the rigging-up I was after advice on. The stuff I can't easily find on the internet.


I don't really want to spend more money on the charger than I paid for 4 batteries, but thanks for the comment.


I already looked, I thought someone might know better.


Would an old phone charger do the job?  There is circuitry in place to prevent over-charging of the battery, but I don't know if it's in the charger, the phone, or built into the battery itself.
Crack open the wire that goes to the phone, get at the wires and fashion a couple of probes to touch to the contacts of the battery.

Maybe fashion a simple docking-slot to hold the wires in place?

I've got one somewhere. The only difficulty with that is the charger has two terminals and the batteries have 3. It appears that these things have two 3.7V outputs, but I'm not too sure of the actual construction.


Time to break out the voltmeter, see what those contacts do...

I did, they were GND 3.7V and 3.7V, don't quite know why it's like that.


Just a thought, attach a load to the gnd and one source, see if they both drop. Maybe a dual battery in a single case, or two terminals for different model phones?

It's for a camera, the terminals are there to match the camera. Maybe one is reserved for the flash unit?


.  Do you have 7.4V between the two 3.7 terminals? Is that + and - 3.7V relative to the ground terminal? Or are they both + or - (relative to GND)?

My sister's camera uses those batteries and I recognise the charger from it, but she's at uni at the moment so I won't be able to get my hands on it until next weekend. Her camera is an EOS 400D if that helps at all.