Reboot loop, won't turn on while unplug. What is the reason?

Since I moved Thailand (pretty hot and high humidity) for a while my Macbook started to do strange things:

• First stopped to work one key on my built-it keyboard.
• One week after next key stopped to respond (arrows down and left). There is no service on this island and it's not so important keys for me, so I decided to continue use it cause I need laptop for my work everyday.

But recently it started to reboot by itself. Time to time. Then it started to do it every time once it's been unplugged from a power adapter, immediately of after 5 minutes work.

Time-to-time the date and base sound settings are getting reset after reboot. Reset PRAM and SMC didn't make any effect to my situation. According any parameters my battery is still in a good shape:

Charge Remaining (mAh): 7517

Full Charge Capacity (mAh): 7694

health: 91%

cycles: 938

Condition: Normal

it's get charged and the battery indicator shows that battery is fine. Any diagnostic tool shows that battery is ok.

Also apple hardware test result was like: "No problem were found"

I suspect that the problem is in PRAM battery. But I'm not sure, cause sometimes laptop rebooting even when it's plugged in power adapter. Also when I'm using FanControl software and making my fans work on maximum speed laptop may work without charged for some time before reboot. After reboot It's able to turn only if it's plugged in. So maybe the reboots are somehow related to CPU temp and the activity of my laptop. If it just shows the desktop and nothing happens it works even without charger connected. Sometimes it's get reboot even when CPU temp is about 60 and every time when it goes about 95.

Inside laptop seems to be ok, there is not anything strange on the mother board, no dust in coollers, coolers are working fine.

Could somebody can offer how can I fix this reboot problem, it the reason in PRAM battery or it might be something different?