On 2/12/2019 2:18 PM, malua mada! wrote:
On Monday, February 11, 2019 at 9:58:01 PM UTC-8, Mike wrote:


I took the bad one apart. Turned out to be a balance problem and the
battery management shut it down. Balanced the cells and now it has been
working fine since.

I didn't buy the charger. I just charged 'em at low current to 8.2V.

I just had a 9v EBL commit suicide in an old Fluke thermometer that has no low power shutoff. zero volts battery now at the terminals.

Took the battery apart. Both 702335 cells have 3.2 VDC and are wired in series... how would you "balance" that?
Positive side is connected straight to the connector. Negative side I can follow to an 8pin IC at pins (2,3) whereas opposite pins (6,7) are connected to where the power needs to go.
A wee little jumper perhaps?
The IC has no markings I can see... don't even know where number one pin is.
Measured ohms between the input and output pins and wouldn't you know it now it decides to conduct and I get voltage at the battery terminals. Darn.
THe question was going to be: how stupid / dangerous would installing a jumper be?
The voltage measured zero because the BMS shut it off.
The ohm meter put enough volts on the BMS to get it to turn back on for
charging.

I can't think of any place a jumper will be useful.
Don't even think about shorting the BMS chip.
The cells are protected against under/over voltage. You need all that.
My limited experience with this battery is that it shuts off charge
when either cell reaches 4.2V.
I prefer to quit before that, around 4-4.1V/cell

Cells are probably matched, but still have significant differences at very
low voltages below the BMS cutoff. It's easy to get some imbalance down
there.
I'd charge it up to 3.8V/cell or so and then check balance and correct if
necessary before proceeding with a full charge.

Thanks anyways
Fritz
believer in fixing by posting questions

This is what's inside mine.

https://imgur.com/pAjauT7

I poked a tiny hole in the side of the package so I could poke a probe in
and access the point where two batteries connect in series.
If I ever need it again, I can use that and the two 9V terminals
to charge each cell individually to 4V. I'm hoping that the
battery will shutdown output at a voltage higher than the voltage
that prevents charging. Not had to test that yet.

Maintaining balance is a proactive activity.
It's been three years. Probably should open up all the meters
and recharge 'em.