KT17 engine Starter engages fine, but no or slow crank
 

HI folks.
KT17 engine. Replaced the Battery a few months back. Old battery was 3 years old and finally quit late Winter. 3 years ago I deleted the key and put in a push button to energize the relay. It's been working fine. What is happening is I Push to start the engine and I hear the starter kick out and engage the flywheel but then it sits there and groans a second. Sometimes I have to release and try again but sometimes if I hold it in the Start position the engine will crank slow and then get faster. It almost seems like the battery doesn't quite have enough cranking Amps. Might this be typical for the K17 starter needing a little rebuild? The new Battery was doing fine for two months, maybe it's not a good battery. Even after the tractor has run a bit, try to start it and usually the same thing. This engine normally starts immediately after it has run a bit. Wire from Relay to Starter has been upgraded to a larger wire 3 years ago so I doubt it is a voltage loss there. any thoughts?

Check your battery connections/grounds, if no joy, see how it acts with jumper cables to a good battery.
if no joy, go right to the starter post with the + jumper cable and see how it cranks, if still no joy pull the starter and inspect/repair/replace.

After I wrote this I headed to the 782 with Meter in hand. Battery stays on trickle whenever not in use. Battery had 12.5ish before cranking. during cranking battery fell to 10V at the Batt terminals. I'm thinking the new battery is not holding up well under load. thoughts.

Ol George. points taken I did not parallel the battery with a larger battery yet. The connections to battery and Relay and starter are all solid and good with 3 year old wires. I think I used 6 awg.

A voltage drop while cranking is not surprising. Voltage is like pressure in a hose. If you measure the pressure of a water hose and then open the hose the pressure will go down. This sounds more like a weak starter, either dirt/gunk/wear affecting the brushes, or some coils shorting out in the armature reducing the magnetic field generated to interact with the magnets to generate enough torque to turn the motor.

I just worked on a tractor that was doing something similar, and I tried jump starting it to the post, and that finished the starter off with sparks and smoke. I took the starter apart after the fact just to look at it and the coils inside were melted and coming apart.

A fully charged 12 volt battery should read 12.6 volts at rest, no load. At 12.5 volts you only have an 85% charge in your battery.