You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
Mines on 75% . I can pay a dodgy looking man a £100 to get it changed or I could have a go myself.
Videos I've seen show them heating a mat to exactly x degrees ,then hurriedly whipping it apart and fitting.
Is it something a numpty could reasonably do themselves?
If so ,what is a good brand of battery?
They are not built to be serviced sadly so lots of bits are glued together hence the heating to melt it. Its probably easy if you've done a few though.. How much would Apple charge? You'll probably get a replacement iPad.
You cannot buy genuine Apple batteries so anything else will be a lottery as to how its going to perform.
Have you spoken to the apple store? When I had a battery changed I think I paid about £40?
Apple charge £99 for a battery replacement. I’d do that.
What's the deal with the iPad servicing?

Do you effectively trade your old one in?
I've got a mini 4 would I end up with a mini 6?
An Apple battery on 75% is probably still of higher reliable capacity than whatever eBay special a bloke on the market is likely to fit.
I’ve got a mini 4 would I end up with a mini 6?
If you didn't, a quick glance would suggest that those prices are about what you'd get if you sold it at CeX and bought a Mini 6.
If it’s just the battery you need replacing I think Apple charge £99.
I've done it on a first gen iPad Air. If you can get Apple to do it for 99 squids then that is really the way to go. For mine is was going to be 400EUR so worth trying. The shop I asked first couldn't guarantee they wouldn't break the screen and they were right, I broke it. I had also thought that was likely and priced it into the decision so even with a new screen it was still much cheaper than a new device
If you want to try it for yourself, and why not, then my words of wisdom are
Buy the battery from iFixit. Battery is good quality although still not as good as an original
Their heavy duty suction cups are nice as getting a good grip on the screen isn't easy
You can do it with a hot air gun rather than buying a heading pad. The trick is to get it really quite hot - 60-80deg. That's hot enough that you can't hold your hand on it but won't burn you. I kept my hand near the screen all the time so I knew I wasn't burning it. I was probably on the 60 end of that rather than 80. When it's hot enough the glue comes apart quite easily
Guitar picks are good enough to separate screen and back but something a bit longer is useful to detach the battery as that is the difficult part.
Read not only the iFixit instructions but also the comments on each stage as that is where the real information is. The big mistake I made was pushing the guitar pick in too far and that separated the screen and digitiser. If I'd properly taken note of the comments I would have marked a maximum depth on the pick. If I'd done that I wouldn't have broken the screen.
It's really not too bad a job and quite satisfying if you like fixing things.
When you say 75% what do you mean? I can’t find any battery health indicator on mine. Do you mean it only goes to 75% on a full charge? The way to fix that is to let run down completely then recharge it and you should get back to 100%.