iPad Pro Battery replacement

Hi,

I'm a little confused about Apple's battery replacement policy in the UK (iPad Repair – Official Apple Support), particularly with regard to the iPad Pro 12.9 5th model.

If my battery health is very low in the future and needs replacing out of warranty, how much do I expect to pay for it?

There's a general service pricing listed at the top (about 600 GBP) but also a battery replacement charge listed for "eligible" ipad models at 99 GBP. Would I just pay the latter? Under what circumstances will you replace the battery for the 99 GBP?