I have 4x 4.0s, 6x 2.0s, 3x 2.5s, and a 5.0 and they're all fine. My oldest are ~6 years old12 volt Milwaukee battery have a bad track record with me. I had 4 of them go bad from ONE battery in the bunch going bad. I opened them up and charged the bad one hoping to balance the pack out, but all four went bad again after two tries and had to throw them out. Kinda peeved, when I had to throw away $350 in batteries. And they were not overly stressed. Just junk batteries or charging system design for that 12 volt setup. All my 18v are ding fine.