Educated guess for lithium charger circuit ?

Thread Starter


Joined Nov 29, 2005
A five cell battery pack salvaged from defunct equipment has three terminals.
One is permanent (+)
The second is mosfets switched to battery (-)
The third is some control/sensor/something, that may allow charging.

How would you guess what to apply to the third terminal C in order to enable charging the pack ? a resistor to (-) ?
Original charger or equipment not available to measure anything. Pack works beautifully well repurposed, want to keep it healthy.

On image, the three terminals are at bottom, the 5 cells are under the board, schematic with not much detail, mosfets by heat sink...



Joined Jan 27, 2019
The third terminal is probably the thermal sensor. Pin 10 seems to be an analog input, so that would make sense.

Thread Starter


Joined Nov 29, 2005
Teach me your rationale, please.
Is terminal C being the battery temperature signal outputted towards the charger telling to provide power because it is within specifications ?


Joined Jun 5, 2013
Lithium batteries often have a thermistor built in that is monitored by the charger to keep it from overheating.

But we have no idea what the board is. Is it not the chargie could controller for the battery pack?


Thread Starter


Joined Nov 29, 2005
Thanks. Everything here is guessy, as we do not know details; it is OK. Thermistors are usually lodged among cells to tell the microcontroller on board to allow recharging/discharging or wait until cool enough. Not necessarily outputing a signal to something outside the pack.
The board pictured attached to the 5S cells is supposed to control balancing, charge and protect from over thermal, over discharge, overcharge... and whatever is typical. But I have seen packs that present a certain fixed resistance related to the 'number of cells in the pack' to a "C" kind of terminal that is read by the charger as 'size' or even 'brand' to accept or refuse charging.

It can get confusing; we have 4 major parties
-5 cells in series
- a charge-protection controller
-a charger or power supply
-a device that runs from the pack.

A similar but not the same! circuit, has no 'C' terminal, just to show it :
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