Charging HP Prime G2

[matalog]

Does a G2 HP Prime definitely charge fine while turned off and plugged in?

I'm pretty sure that I have left mines on all night, while turned off, on the USB wall charger I have, and found that the lightning bolt was still there when I plugged it into a PC and left it on the next day. Whereas when I leave it charging and turned on, on the same PC, after a certain period (much less than 8 hours (which is all night)), the lightning bolt will disappear and show that it is fully charged.

After the full charge while turned on, the bolt will not appear until it has run down a bit since that full charge, or been used without plugging in.

Has anyone else experienced anything similar? This started when I was only charging with the device turned off, which I assumed would charge faster, and given that I use the calculator for a lot of the day, I thought this would be better. I only noticed there may be something awry, when the calculator was struggling to last even one day, whereas, now when I charge with the device trned on, it doesn't drop below the initial 25% in one day, and remains to appear to have 100% charge.