Last week it was up to 100 outside and my alt. was only charging 13.4 volts. Hooked a load tester up and it showed 13.6 so I kicked it in. It dropped but popped back up to 13.6. Why was voltage reading low?

 

the voltage is adjusted according to batery temp

there is a sensor under yer drivers side batery that reads the temp

 

Same thing happened to me with the '06 this weekend too. It was doing a full charge when I left home because it was cold out, like 50'F. Stopped for fuel after a couple hours of driving and the voltmeter was left of center (11 volts-ish), I turned everything like lights, heater and radio off. Stopped and restarted truck and no change. I was going camping, pulling the toyhauler, and figured the alternator died and the truck batteries were feeding off the trailer batteries (?). Got to site and tried starting the truck again and it started fine. Last night there I plugged the trailer cord into the truck over night and took a voltage reading of 13.2VDC on the truck batteries in the morning (after sitting for five days) and I know my trailer only charges at 12.5VDC. Started the truck to leave and all was fine again. The belt is new. So.... alternator? voltmeter? quirk?

 

these systems are wierd but they work run em and watch em

 

Just a bit ago found out that the regulator drops the voltage in hot weather to keep the batteries from over charging. Sound about right?

 

What he said...