I made a really stupid mistake and left my batteries connected to the chargers while I was away for a month and not flying.
They were safely at storage voltage, 3.85v/cell. I have four dual channel chargers and the chargers were plugged into a power bar that was switched off so I knew there was no way they could be charging.
I knew one of the chargers was flaky but it did not occur to me that it could discharge a battery even though the charger itself was not powered up. The switch was on but the charger was plugged into a power bar that was switched off. The power was off. So when I get home, that battery is showing 0.5v on all cells. The other seven batteries are fine. Sigh - $250CDN goof. Arrggghhh