I still recommend removing the old NiCd battery before it leaks.
As for fitting a replacement, there are much better things to spend your time and effort on IMO.
Like
- Checking to see if you have any Zip RAM and upgrading to 16Mbytes FAST RAM.
- Checking to see if you have all the latest chips: Buster -11, DMAC -04 & Ramsey -07, SCSI -08 and KS3.1
- Buying & fitting a SCSI->IDE adapter
- Buying & fitting an IDE->CF adapter in the spare floppy bay. Makes it so easy to exchange files with the PC