Got in the plane the other day and went to crank - prop turned slowly and wouldn't start. Figured the battery was done as it was 6yrs old got a replacement PC680 dropped it in same thing. Cleaned all the connections on battery, ground to engine, ground to airframe, relays, etc. Ran voltage at battery 12.8, ground 12.8, relays 12.8 (no load) went ahead and replaced the starter solenoid as it was old to. Checked voltage at battery while cranking went to ~6V, obviously that's the problem. Question is besides starter (delco remy) is there anything else that could drop the Voltage like that?