Using an old mobile phone as an universal Li-Ion battery charger

About using an old mobile phone as an universal Li-Ion battery charger

I have an old Siemens mobile phone that uses a 700 mAh, 3.7V battery like this:
https://www.amazon.co.uk/Li-Ion-battery-suitable-Siemens-Gigaset/dp/B00BU24ETU (see also the attached picture)

I also have an unused new 670 mAh, 3.7V Digipower BP-70A digital camera battery.
See: https://www.digipowersolutions.com/product/88/battery-replacement-samsung-bp70a-bp-70a.html

Both Li-Ion batteries have 3 contacts: plus, minus and a third one in the middle. Unfortunately the contacts are located in different positions and I can not simply fit inside the Siemens phone the BP-70A battery and see if it is charged. I need to run wires from the plus, minus and the third contact of the BP-70A battery to the corresponding pins of my phone.

The question is, will the Siemens phone charge the BP-70A battery, stop in time when it reaches full capacity and latter the same phone be able to use this battery as if it is its own original power supply or this arrangement (trick) will not work?

It depends. On some batteries that third terminal is a thermistor for monitoring battery temperature; on other "smart" batteries, it's actually for communicating with a chip inside. You need to verify what that terminal is on those two batteries.

barry said:

It depends. On some batteries that third terminal is a thermistor for monitoring battery temperature; on other "smart" batteries, it's actually for communicating with a chip inside.

Click to expand...

This article, talks about smart batteries as devices having 4 or 5 terminals.
The text suggests that most smart batteries have at least 4 wires:
"For safety reasons, most battery manufacturers also run a separate wire for temperature sensing."
It would appear that smart batteries with just three terminals are rare.

tempos said:

This article, talks about smart batteries as devices having 4 or 5 terminals.
The text suggests that most smart batteries have at least 4 wires:
"For safety reasons, most battery manufacturers also run a separate wire for temperature sensing."
It would appear that smart batteries with just three terminals are rare.

Click to expand...

Sometimes the thermistor is totally isolated from the cell, so you have 4 wires for a single cell.

Batteries with several cells in series usually have a tap at every cell in order to allow for monitoring and limiting each cell's max. charge voltage (to 4.2V).

I think your idea of charging the camera accu by the Siemens mobile phone should work well.