Cordless tool battery pack discharge byself in one week

dejanc

10 µW
Joined
Jul 5, 2017
Messages
5
Hi Members,
I've replaced obsolete 18650 battery cells on battery pack 1813 model. Old batteries was 1300mah >> I have put 2850mah, and with little more amps. Replacement was nothing special, and also no problems with charging. Also the grass line trimmer works perfectly. Already four times without any issues. And the battery capacity indicator was still show 2 green lights of 3.

Last time was charge battery, so it Will be prepared within next 7 days >> after 7 days I was suprised the voltage drops to minimum. The battery was not inserted into cordless tool, and was just puted on storage shelf.

Does anyone have any idea why the battery pack discharge byself?
I'm mean, only thing what is inside of the package is BMS. Is possible the circuit discharge it?

Thanks in advance for any info.
 
Open it up enough to measure cell groups and look for one drained into the low 3V region? If the BMS uses balancing circuit there's a strong chance the bleed resistor is somehow turned ON thus killing the attached cell or group. Shorted balance switching transistor is common problem.

When you have it open post all the cell/group voltages - 18650 cells should be around 4.2V fully charged. A pic or two might help as well....
 
maby you connect the B- B+ first and later the bms plug on the bms board? smal ballans fet-resistor can damage and drain the cells empty
 
Thanks for feedback. Will open it, and checked what is happening.

Thanks for tips, which I Will follow them...
 
999zip999 said:
? Joachim You must hook the sense wires first ? I have hooked up the main wires first then lugged the sense wires in.
so you say first main wires B- B+ and later the sense wires?
 
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