John Piddock

HI I went to start my xj600 this morning after being away for a month. Absolutely no juice from the battery. I put it on charge and very quickly the charger read full. I replaced it back in the bike but it was still dead. I then decided t jump start it from the car and it started fine, I eventually disconnected the jump leads. I left the bike running for another 30 mins then switched it off. Went to start it again and the battery was dead again. I know this is probably a stupid question but have I got a dead battery? or could it be something else?