So i have recently purchased the bike in question - 1996 Yamaha XJR400 and within the first week, the battery went flat. Pulled the battery to charge it only to find it had blown up into a balloon. Figured it had lost charge for this very reason and went and bought a new battery. So here we are, nearly 2 weeks later and the new battery is flat. The kicker is i had just done a 100km round ride, left the bike for a couple of hours and when i went to start it again, it was flat - nothing had been left on. Had a couple of turns in it but that was that. Gave the bike a push start, went for a ride (~20kms), and the battery easily had enough charge to start the warm engine again. I thought i might pull the battery and stick it on charge but the battery itself was bloody hot - i wouldnt have thought this to be normal?? So, what would be the problem?