Here is what I have:
5091000 Snapper Fast Cut ZT18440KH, 18HP Zero-Turn Rider with 44" Mower, I know this because I used to have a basic manual.
It has a Kohler motor on it. I have to assume it's an 18HP because all of the Kohler Identification that I know to look for is gone.
Here are a few pics:

My issue is electrical. And it has to be something related to the charging system. Here is my reasoning:
Just bought a new battery, (the old one died VERY quickly and I just thought perhaps we left the key on). The new battery starts the mower just fine. Twenty minutes into mowing the motor just shuts off. In this case I was able to fire it up for about 20-30 seconds after turning off the blades and letting it sit for a minute. But then it just shuts off again. Leave it sit for 30 minutes and it will run for 2-3 minutes now.
So, I'm capable of replacing components, but my issues are:
1. I can't figure out EXACTLY which Kohler motor to buy components for since my Kohler ID tag is gone.
2. I am unsure of which electrical components I should replace, and in what order?
3. Does anyone know of some good videos or tutorials on how to replace these components?
Hope y'all can help out!
Thanks!