Titi matey unless you fancy getting a cheapo generic charger from ebay which is probably a waste of time anyway, I'm comfortable writing that lappy off. Usually internal charging issues are the motherboard, so.... Time for it to sit on a desk, always plugged in
Been having similar problems with my laptop battery, a Novatech. Laptop can cut out without warning when on the battery; flashing red power light when charging (didn't used to do that). I've tried to reset the charge meter on the laptop so I get a more accurate reading of the battery but it hasn't helped - usually cuts out somewhere between 24-38%, so I'm always flicking the mains on and off.
Just need to suck it up and order a new battery. It's probably come from hibernating it all the time instead of turning it off.
Aye, all that suggests the actual capacity is changing, Windows is just playing catchup, and kudos for realising that means the battery is offski.
I let my laptop die, hibernation is not an issue to worry about, in my experience and research. I have a generic secondary battery I swap with every so often. Dirt cheap, I don't mind generic, as long as the voltage is right...
The worst thing to do for a battery IMO is to keep using it on full charge connected to the power. Because you're not actually using the battery and it will degrade quicker. Even Windows 10 has pretty smart power management features but you wouldn't be giving them a chance to work from always plugged-in! Batteries work best when they can breathe.
... I need a job