I never got very good life from my Minelab re-chargeable battery packs. Usually lucky to get 6 hours of hunt time even with the 1600 mah pack in my Explorer II. This may have been my fault as I may have not been charging them long enough. The Minelab charger is only 100 mah and usually takes a full 24 hours or more to fully charge.
The re-chargeable packs also have a limiting circut built into the pack so you can't just use a charger with a higher output charger.
With the SunRay base ($21.25 with shipping) you are charging through the battery contacts and are not limited to a certin mah. The base's input plug is a different size (1/4" I think) and does not accept the Minelab charger plug.
RunRay makes a charger but it's out of stock and being re-designed. You can buy a "universal" charger 500 - 600 mah from WalMart, Radio Shack, ect... with mutiple size plugs that should do the job.
I've been using the "standard" battery pack with 2500 mah cells and don't have to worry anymore.
HH
Jeff