In digging into those suggested above they are all 3" or more longer and most are 2" wide and more thick than the wm10 can handle. The ones that will actually fit inside are smaller mAh, like 300, 350, and 600. Even the 800 and 850 mAh ones are too long most of the time. It has to be 2" or less long, 1 5/8" or less wide and less than 5/16" thick.
The old postings on here only suggest similar searchs but after aboput 10 hours of searching out 3.7v batteries and Ah ratings, I finally sent an email to MINMAX southern area in Lewisville Texas for help[. They built it so maybe they can help without paying 10 times the barttery cost to get it replaced. Got another email from Minelab service and she may have a solution for me. She is a super Minelab Customer Service asset!
It is really as simple thing, take out 4 screws, lift the cover, pull the battery connector out and put a new on in, put cover back on and screw it down. Too bad there it is such a difficult size. Tons of RC Quad Copter and other model stuff out there but just not physically the small enogugh size. I just had a brain wave, it dont have to fit inside the box! It could be connected and attached outside the box, maybe wrapped and insulated. I always carry it around my neck inside a plastic waterproof wallet/document carrier anyway. Would look a bit Southern Engineered but better than tossing a $250 wireless or paying a ton to get it replaced.
Thanks For the assistance.