Warning lights electrical problem

I've just been to start me bike after finishing some bits but she hasn't been ran in bout 3 months so i knew the battery was going to be dead but i hooked it up to a mates bike with some jump leads and everything did seem ok but first of all when i pushed the bike along with just the ignition on the speedo was reading differnet speeds and then when i started it which it did fine, its reading no rpm, the oil/coolant light is flashing and the red diagnostic light on the rpm gauge flashes slowly. Now i know the rpm is working as i have just adjusted it on the TPS because i've just fitted new carbs, the oil level is fine. The bike will run fine but after a few mins the revs rise and then the bike dies and theres no battery power at all, i have done no electrical work at all, theres only been new carbs go and and a few plugs unplugged then hooked back up again, could it just be a completely duff battery causing all the symptoms? Any help much appreciated!