Notebook causing battery to overheat after charging to 99%

I have a Samsung N150 notebook with Win 7 starter.
It is not a battery fault because I have checked using a second exact same notebook with identical battery and both batteries charge fine to 100% (fully charged) wthout heating on the second notebook.

However both batteries overheat after 99% (charging) on the faulty notebook.

Never had battery charging problems until a week ago when I noticed that the battery was getting very hot.

Prior to this without exception it would charge up to 100% and indicate "fully charged" - with no heat.

Now it charges up to 99% and indicates "charging" instead. If I keep the charger plugged in after reaching 99% the battery gets hotter and hotter within ten minutes and never indicates "fully charged".

Why not use the other notebook? Because in other respects it is not as good as this one.

That's a good suggestion, I'll try it if the problem crops up again.

In the meantime I accidentally dropped the notebook whilst in its soft case, my instep broke its fall instead of the road and now the charging is back to normal- Fully charged (100%) - without any heat.

Maybe the jolt jogged something, the notebook was in sleep mode at the time, I'd just been using it in a restaurant.

My foot was also O'k :)

Not a comprehensive solution I'm afraid , because I haven't a clue what the mechanics are for the charging going awry in the first place, either hardware or software related?

It is mainly behaving itself, but has failed to complete charging and became hot a couple of times when
the notebook is running.

It is worst when switched off and charged, then it overheats every time and at an earlier stage of charging,
from around 80%.