Bought a Refurbished xpal power case online. How well do they work?

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http://forum.xda-developers.com – I just ordered a refurbished xpal power cases online. It like $15 shipped to canada so it wasn't as bad as the $75 brand new. The ebay seller sold alot of them and had alot of feedback saying good thanks etc. What do you guys think of them? Lets say if the battery craps out is it possible to replace it myself (HowTos)