From the terms and conditions of Makita's 3 year warranty;
The guarantee does not apply where Non-genuine or recommended parts or accessories are fitted to the tool(s).
Having studied Law of Contract at Uni, I'd say that's a pretty watertight get-out by Makita if they don't like you using somebody else's cheap batteries, whether the batteries were related to the cause of any defect or not. They don't need to prove the non-standard batteries caused the fault, if its in the terms and you buy the tool, you are bound by those terms. They'd argue if you don't like the terms of the warranty, its your decision whether you want to buy the tool under those terms or not and you can always buy another product from someone else if you don't like it. I'd say this is a fairly standard clause most manufacturers put in their terms, to try and ensure they get the max money out of you; don't buy our quite expensive extra bits and you'll regret it if it goes wrong, 'cos we want all your dosh. Of course if an item did go wrong and you'd been using non standard batteries, you could just borrow a genuine battery from a pal, put it on when you take the defective tool back, and they'd be none the wiser and have to repair it.
