phone battery contacts and charging question

[paulr]

Phone batteries usually have 3 or 4 contacts but often only two of them do anything. But I notice that the Nokia BP-4L really has different voltages going to the contacts. The middle contact (when the cell is near empty) is at 3.3 volts but the outer one is only at 2.9 volts or so. Question: what do the three contacts do? I have one of those clamp-type universal chargers that has worked well with other phone batteries, but doesn't seem able to charge the BP-4L. Thanks.

 

[csshih]

there should be a protection circuit built in which also checks the temp, etc, of the cell.

 

[Lynx_Arc]

Phone batteries usually have 3 or 4 contacts but often only two of them do anything. But I notice that the Nokia BP-4L really has different voltages going to the contacts. The middle contact (when the cell is near empty) is at 3.3 volts but the outer one is only at 2.9 volts or so. Question: what do the three contacts do? I have one of those clamp-type universal chargers that has worked well with other phone batteries, but doesn't seem able to charge the BP-4L. Thanks.

http://cpkb.org/wiki/Nokia_BP-4L_battery_pinout

 

[neoseikan]

My PDA cells has many more pins. I really don't know why.

 

[paulr]

http://cpkb.org/wiki/Nokia_BP-4L_battery_pinout

Thanks! That is informative and it indicates that my digital voltmeter has rather lower input impedance than I'd have expected.