I have a Scag Tiger Cat that is a couple years old now. This past summer the voltage regulator lost good ground and it drained the battery. I fixed the bad ground at the voltage regulator, let the mower charge the battery, and didn’t have any more trouble. It had been a couple months since I’d ran the mower, so today I decided to start it up and allow it to run for a little while. Well the battery was dead (around 10.5 vdc), so I had to jump it off. Once I had it started, I removed the jumper cables thinking I’d see if the battery would take a charge. As soon as I removed the cable, the engine died. I figured I had a charging issue again, so I removed the voltage regulator, cleaned all of the contact points and put it back together. Still no joy. Soon as the jumper cables are removed, the engine dies. Certain that the engine should run once started, regardless of the condition battery (or even without a battery), I began trying try to diagnose what I thought was a charging system problem. Well, it appears to me that the charging system is functioning correctly. With engine off and ignition on, I have battery voltage on the purple wire (center) at the voltage regulator. With the engine idling, I have 13.09 vdc on the purple wire at the voltage regulator and 15.0 ac on the stator wires. At WOT, I have 14.43 vdc on the purple wire and 37.8 ac on the stator wires with the voltage regulator connected. With the voltage regulator disconnected, I have 45.8 ac on the stator wires. But still it dies as soon as I disconnect the jumper cables. I could have sworn that earlier in the summer when the battery was drained (at an even weaker state than it is now) that it ran fine with the battery disconnected once I fixed the bad ground at the voltage regulator. Was I mistaken? Is there some circuitry on these machines that requires a battery in order to keep the engine running? Just to check, I disconnected the battery completely, started the engine with jumper cables and soon as I disconnect one of the jumper cable leads, it dies.