so i was going to get some lunch today during work and on my way back the truck chimed, looked down. and it says check gauges. no cel light. look over at my volt meter and its at about 9. got to work and shut it off. then after work started up kinda slow drove 30 miles home never went up. never went down. got home checked all my fuses, battery connections are tight, checked the grounds to the block and they are tight. what do i do next. there does appear to be battery acid on top of my one battery. what would cause this or any suggestions as to what to do. thanks in advance

06 cummins, quad cab, 6 speed.

 

I'm a little new to diesels but usually that would indicate 1 of 2 things. Bad battery (disconnect the leads and measure with a meter. Should be ~12.25 volts). Or could be alternator/regulator.

While the truck is running put a meter across the battery. If the voltage is ~13.4 volts it's probably not the regulator/alternator as long as the heater grids aren't cycling.

I would take it to your dealer and let them determine root cause but having this info will help you be informed.