3 pin li-ion batteries

[Holger Barske]

I am looking for a battery +/- 5V supply.
The idea is to use those unbelieveable cheap cellphone li-ion batteries and the appropriate chargers.
The question is: what to do with the 3rd pin of the li-ion battery? Does anybody know how it is connected?

[eeka chu]

The newest Li and Ni-MH batteries actually require some fairly complicated sh1t going on to charge them.

They go thru quite radical temperature changes whilst they charge and require thermal protection to make sure that they execute the charging correctly.

The third pin is most likely some kind of in-built thermal regulation pin. A lot of Li / Ni-MH packs have a thermistor somewhere in them to monitor the temperature of the cells as they reach their full charge.

Have a look on semiconductor sites, like Maxim's, for 'battery charging' and so forth.

Maxim sell a number of IC's specifically designed to monitor the charging of Li and Ni-MH cells.

You shouldn't really just put them straight onto a ...whatever...Vdc supply and try charging them blind.

I'm interested in the LM3647 since it seems ideal for the kind of Ni-MH pack I'd like to use. It also charges Li packs. Check it out.

If you send me your email address, I'll mail the PDF to you.

You should be able to tell if the third pin is some form of thermal regulation as it's resistance will change if you subject the battery pack to a temperature change.

Put it somewhere cool for a while, check it's resistance, then warm it up in your hand and check it again.