GT275 engaging blade problem

[moplady]

I am having problems with my John Deere GT275. Usually I have to jump start it as the battery is always dead. Replace the battery and it was great for about 2 mowings, then had to jump start again. Now when I jump start and go to engage the blades the blades will not engage. Jump started again left the battery jump cable connected to my truck battery and the blades will engage and run prefect, take it off the jumper cables and the blades will not engage So what do I need to replace? The solenoid ? As I know a new battery will not help.