My 08 Sporster died at the end of last season. I had always kept it on a trickle charger but the battery was old. Fast forward to April this year I removed the battery and the negative terminal (on the battery) was burnt off. I replaced the battery and left the trickle charger off. I bought a battery on the cheaper side off the internet and I talked. I cranked the bike and it ran great for 3-5 mins, so I **** it off. Two weeks later I went to ride and the battery was dead again. I took it off and tried to charge the battery, but it wouldn’t take a charge. I haven’t bought a new battery yet I am just curios as to what could have caused the burnt negative terminal and if this has something to do with why the new battery was messed up.

 

Burnt or melted terminals are usually caused by a loose connection.

If your cables are good the second failure is most likely unrelated. I'd check the cables and charging system.