LiPo cell overdischarged (down to 0.7V) [charges just fine]

Thread Starter

flasergames

Joined Aug 21, 2022
2
Hello,

I am currently re-purposing my old powerbank for a robotics project (BMS and LiPo will be integrated into a 3D printed case).
The Powerbank (CellularLine FreePower Slim 5000) was unused for 7-8 months and while opening It,
I measured the cell voltage, which turned out to be ~0.7 V!

Normally I would think that this LiPo should not be able to be charged by the powerbank's BMS anymore,
but the powerbank BMS (IP5306 | Datasheet PDF here) charges is just fine.
While charging from 0.7 V to ~3V, the charge current was around 0.15 A.
When the cell voltage reached 3V, the current increased to 1.6 A.

Is this LiPo and BMS safe to use?
I would assume the cell should not be able to be charged anymore.
Btw the LiPo is not puffed or deformed (yet).
 

Thread Starter

flasergames

Joined Aug 21, 2022
2
I want to play it safe and disgard the LiPo after all that I have read now.

But it still makes me curious why it still charges fine and seems to work, despite the low cell voltage.
This type of powerbank is very common here in germany and is/was sold at big electronic stores and supermarkets,
and I bet I am not the only one who charges this powerbank after a long period of non-usage.

The used BMS is also a common choice for manufacturers, but why does it fail to deny charging at low cell voltages?
 

Ya’akov

Joined Jan 27, 2019
6,853
The low cell voltage can be a problem but is not necessarily one. If no internal shorts formed (and clearly they haven't) then the battery is safe as any other. You would know right away if the undervoltage (≤2V per cell) condition had become dangerous because the charging wouldn't work and the current, if applied would result is heating the battery and not increasing the terminal voltage.

Or, if it did work like yours has, the self-discharge rate would be much higher. For safety, you would want to be very vigilant about not letting an undervoltage condition to occur again because if shunts had begun to form, they would form much more quickly if the conditions permitted it.

If you don't need to salvage the battery, it is, as you have determined, a good idea just to discard it. You probably could use it safely but if the risk is not required, you are sensible to eliminate it.
 

BobTPH

Joined Jun 5, 2013
6,065
Is it possible that an internal protection board has kicked in? I have seen cells with protection jump from a reasonable voltage to a very low one like that when the circuit cuts them off.
 

bassbindevil

Joined Jan 23, 2014
628
Power banks often have protection chips as well as the main chip. So maybe those did their job and disconnected the cells to protect them. Or if it had a pouch cell, that could have a separate protection board. But, I've come across 18650 cells in a battery pack that were down to near zero volts, and seemed to recover perfectly after a charge. As in, same discharge mAh as cells in the bank that hadn't been over-discharged.
 
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