We'll I came to this thread with some very strange battery issues. For starters - this is a new Variax with original charger and original line 6 battery. The battery worked fine for about 3 recharges, then on the 4th full charge the guitar lost power after about 1 hour. Nothing, no 4 green lights, no flashing single green light. Press the test button and no lights. I charged the battey and the red charger LED was blinking as though it was fully charged right away. I tested the battery and it read 8.46v - or fully charged. I tried leaving the battery on charge overnight, I also left it in the variax overnight - no sucessess after each of these steps. I then planned to take it in for service. So I left the battery in the charging cradle "not plugged in" and waited a day or so to take it in for service.
So now I'm at the service centre and we do a quick test to see if the battery is good. My battery powers up another variax just fine. So now I'm sure it's my guitar right!! ... just for kicks I plug the battery into my guitar... and.... guess what, works fine!
You might be thinking that it's a loose wire in the guitar, but I assure you, I had the battery box out, wiggled all connections, and nothing. I plugged the battery in about 50 times when it was not working and all I would get is anywhere from 1 - 3 seconds of 4 green lights, then everything goes dark. And now that it's working - I'm seeing it continue to work regardless of how many times I re-insert the battery. Not looking like a loose wire in my book.
So now, I'm going to watch this closely. It's either 1) that the battery was in the cradle overnight bleeding some current in the battery (not plugged in), or 2) Plugging the battery into the other Variax somehow reset the battery!
As one other post mentioned, I certainly think this is due to some convoluted scenario with the "genuine battery detection" circuitry. It could be that the battery gets a static zap or something that confuses the ID chip in there and it needs to be reset, or there is some other handshaking going on that gets permanently confused until the battery gets placed in another guitar. I should also note that sometimes I use a VDI cable with an HD500 which powers the guitar and I leave the bettery in the guitar. Nowhere does it say this is bad or should not be done, but maybe this causes the issue I experienced somehow.
I know this sounds wierd, but something strange is definitly going on. Hopefully this helps someone. If this happens again I will post back with more details.