good site to obtain replacement battery

[PelicanBrief]

An oldy but a goody I'm restoring. Was given to me in a sad state, no charging lead, flat battery, damaged cover, old out of date apps and no protection. I got a charger and did a factory reset, reinstalled apps I wanted, fitted it with a new folio cover and got connected to my hotspot and it's going well for what I need. The battery doesn't last long now due to having been flat for so long and I'll need to replace it eventually (currently running the tablet with charger connected). Looking for a good source if anyone can chuck some suggestions in please.