Recharging OSTC Mk2 from mains

[gorcio]

Hi,

after 40 dives, it was high time I recharged my unit for the first time. I plugged it into mains with a mains to USB adapter. Everything was ok, and in the end, I noticed red LED blinking twice, signalling charging finished. Now, I switched unit on, and the battery indicator is not full - about 90% (firmware 1.70).
My question is :
is it the battery indicator that's so much inaccurate, or is there one of the cells that's going down ?