Minelab Sovereign GT Battery Questions

Been all over all the forums and can't find an answer...

I think the rechargeable battery pack for my Minelab Sovereign GT is shot and I might have to rebuild/replace.

Two questions:

1. Rebuild: how does the case open? Any gotchas?
2. Replace: the ML rechargeable pack is only rated at 1000 mAh. Modern AA rechargeables are rated at nearly 3X that figure. Wouldn't I be better off buying the alkaline pack and installing modern NiMh batteries?

Thanks in advance for your wisdom.