If it's just the battery then there's the DIY option, a fair bit of info on t'interweb including from our own.
http://forum.tz-uk.com/showthread.ph...ange-pictorial
https://omegaforums.net/threads/x-33...-change.57353/
http://www.horologycrazy.com/2010/12...ry-change.html
If it needs a service personally I'd probably go for an independent. I know that creating a 'Gen 1.5' is a popular modification although it's not for me (I ended up with one of each instead ).