Same issue with my 4500P. Mow for an hour or so and voltage drops into the 12.3 range. When it drops to 12.2 the light and audible alarm sound. Shut mower deck off and the voltage will climb to about 13 volts if the throttle is left wide open. Just one of numerous problems with this 3 year old machine machine. Replaced instrument panel at least 4 times due to fogging. Last one was a newly designed panel to cure the fogging problem. Worked great until the first cool day of fall. Fogs up just like the first 4. I have had at least 3 slope meters replaced. Could be on level ground and the meter will go crazy saying you are on a 62 degree slope. Audible alarm sounds and you can't stop it. I've recalibrated the meter and it will work fine for awhile then does the same thing again. It has been one thing after another since I bought it brand new 3 yrs ago. Now out of warranty with the same issues repaired under warranty. I love the machine and the way it mows but not sure I would buy another because of all the issues. Sad thing is most issues are with things manufactured by a 3rd party and sold to Ventrac. Ventrac doesn't seem to pressure these manufacturers to get their problems solved. Unfortunately it reflects on Ventrac in the end. love the machine but I'm absolutely sick of all the issues that came with it.
