I have some problems testing the capacity of some Lithium batteries from Leica Geosystems

[Darius_bd]

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Hi everyone! First post here. I'm not quite sure if it's the right place to ask this question but this forum keeps showing up when googling about this subject so I thought of giving it a shot.

So, at work we have some Leica Geo 3D scanners with lots of batteries. The batteries type is GEB212 (https://www.sccssurvey.co.uk/leica-geb212-li-ion-battery.html) and they look like it a housing for two 18650.

Some of them are really old, some others were bought used. I wanted to test the capacity of them to see which ones are best. For that I bought a XH-M240 test board in Aliexpress https://www.youtube.com/watch?v=7x1zB3VcX1I

I thought it was as simply to see how much mAh they can output before reaching their low voltage threshold. Since they are rated as 7.4v, my guess is that the threshold should be at 6v, as for a single 18650 would be 3v.

With the help of some cables I connected the batteries to the test board and my problem is that it's reading 6.6v out of them. I tried with fully charged ones and also with depleted ones and they all show 6.6v. I tested a simple AAA alkaline battery and it read 1.4 so it looks like its reading those correctly.

I thought it could be a problem of some BMS inside the batteries so to corroborate the reading I thought of using my multimeter to read the voltage out of both cables connecting to a battery while it's being depleted. I'm getting between 7.6v for the full ones and like 7.2 for the depleted ones.

The test board actually shows the mAh flowing trough it, but since it always reads 6.6v I'm afraid is gonna make the batteries squeeze out all their capacity beyond repair, as it's supposed to stop when it reaches the lower voltage threshold I set.

I don't know much about electronics, I'm just tinkering with it so I feel like I'm doing something wrong. Anyone has any clue what is it?

Picture of the simple setup: https://imgur.com/a/BmSmBTy


Many thanks beforehand!

 

[liveforphysics]

They are 2 cells in series. So 3v would be 1.5v per cell, or much too low.
8.2-8.3vdc should be full, and 6Vdc should be empty.

 

[Darius_bd]

They are 2 cells in series. So 3v would be 1.5v per cell, or much too low.
8.2-8.3vdc should be full, and 6Vdc should be empty.

Thanks for the reply! Indeed I set 6v as the minimum threshold, but all batteries are reading 6.6v, the full ones and the almost empty ones. :?

 

[Jrbe]

It's possible the bms is blocking full output voltage. It might supply 6.6v to allow the device to turn on and say low battery in some way. Or with the low power it can do a handshake with the battery, get battery voltage, then power up.
Your picture is hard to see what's going on.
You might find an extra terminal or more that are the communication lines, that's where the handshake happens.
You likely need to test with a device connected or open one of the bad batteries to test voltage at the cells.