I bought a BL-5J battery, so now I have 2 (and I have marked them so I know which is which ).
I have difficulties charging/using this battery.
What happens:

• connect to charger, it sometimes starts charging for 1-5 minutes, then goes green
• it then sometimes boots succesfully, the battery meter shows full charge
• it then dies unceremoniously after a few minutes - always before I managed to do the calibration dance.

Note "sometimes" - other times, it goes into some sort of boot loop or the yellow light doesn't come on at all.
I tried with 2 different chargers.
I tried a full power cycle, the behaviour wasn't significantly different after that.

If I put in my first battery the device boots normally.
The status bar battery meter shows 0%, but bnf shows 99% (I guess this could be fixed with another calibration - anyhow, that's not the topic of this thread).

I know what the most likely answer is here, but just wanted to make sure if there's something I haven't tried yet?