macbook pro 2011 battery replacement

Hi, I have a macbook pro 13" late 2011 and am debating whether to replace it with a macbook air 2020 with the quad processor. I can't really afford a new mac but need a computer that's reliable because I am a writer. As you can see from the etrecheck my battery count is very very high and sooner or later it will give up the ghost (or will it?). Also my trackpad is playing up again and the cursor is going haywire - I have to use a remote USB thing and an external mouse. I can go on using the mouse and try to correct the trackpad problem with resetting the PRAM etc. but I guess it will probably just happen again.

I could just go for a new battery from megamac which I think are the best bet in the UK. Perhaps this would solve the trackpad problem (I've already changed the hard disc for a lovely fast 1TB SSD one).

Anyway, I know that a new mac would solve the problems but would rather continue with the old one if feasible - i.e. if meltdown isn't probably soon new battery or not. Any advice most welcome.