Not a fail as in a disappointing tool but was a failure. M18 8.0 battery that I bought new failed after 2 yrs. I've been lucky & have never had a power tool fail on me where I had to send in for warranty. MW makes it easy & they replaced it, that was late last year. A month ago my buddy's M18 8.0 also died, same failure as mine (would no longer charge). I sent it in for him & again MW replaced it.
Disappointing cause I bought the 8.0 in fear of my 9.0 dying. But my 9.0 still works fine, apprently mine wasn't one of the ones that commonly fail according to what people say online going by the label type.
I've heard that M12 6.0s tend to fail, so far the 2 that I have are still working fine. Same with my M18 12.0, all of which are older than my 8.0 and are probably out of warranty now.
All six of my M18 5.0s are still going strong, 4 of them are from 2015. Well one of the ones from 2015 wouldn't charge to 4 bars a couple weeks ago. I hadn't used it in a while (forgot to put in rotation). Turned out 2 of the banks were low but not critically low, just lower than the other 3 banks so those 2 banks would never fully charge. I balanced charged all the banks & that battery is working fine again now.
Irrelevant since it's old now but I experienced the common chuck issues on my M18 gen2 hammer drill. I cheaped out & instead of buying a proper Rohm chuck I bought the stock chuck from a gen3 hammer drill. Luckily it has been working fine though. My stock gen2 chuck acted up all the time, I really hated that thing.