I had a similar problem with my old HP ZBook laptop, which I had bought second-hand in Vietnam a few years ago when I was living there: It suddenly started getting VERY hot. I first took it to a repair shop at Seacon Square, and they replaced some little foam pads inside of it - for 800 baht. I'm pretty sure I paid the special farang price for that. Unfortunately that didn't help much at all. Then I bought an aluminum rack (originally meant to be a dish drying rack - from HomePro - which happened to be the perfect size) to elevate the laptop from my table, and that seems to have solved the problem.
The battery also just died, so I will follow the recommendations here - and try to find a replacement battery at Fortune Town. Or maybe I'll just use it without a battery, as I only ever use that one at home.
Finally, my seven-year-old work laptop recently started acting up on me, so I bought a lovely Fujitsu laptop that weighs well under a kilo. I had seen it at the Emporium for around 50,000 baht, and it was love at first sight. (It is made in Japan, and I trust Japanese quality. And it's just so unbelievably light - about half the weight of most laptops.) The deal was sealed when I found it on Lazada for just under 40,000 baht during their recent anniversary sale, and I couldn't be more pleased with it:
https://www.lazada.co.th/products/i3273787395-s12164887105.html