Battery Tester's Diagnostic Journey Unraveling Fluctuations On the Road

Noticed today my volts are fluctuating while RPM's are near or above 2000 on highway trip. At stop light had battery light come on. I installed a AGM battery and with a volt meter I am reading 14.9-15.3 volts at the battery with it running in park. The needle on the dash ... If not enough current is supplied the voltage drops. Also, low idle RPMs and high load (heaters on, headlights on, and... you get it) might be ... Voltage reading on the dash fluctuates as voltage demands change. With batteries that are old and in need of charge, you will see higher ... one more to check if the current is to high for the battery there is a lot off gassing. All the gass bubles are dropping the charge current. When I start my car, my volt meter is showing a steady 13.8 volts. However, once the car heats up, or after 10 minutes driving, it drops to 11.9 ... Some of the battery voltage fluctuation might be normal. Check your owners manual about the special feature your truck has that was designed to increase ... When the batteries need to be charged, the voltage goes up to 14.4v or so, and when it senses they are charged it drops way down, I've seen 12.9 ... Nope. That pretty much sounds like a dead battery. It sounds as though one of the cells has a short in it, which is causing your rapid ... This depends on RPM, speed, temperature, electrical load, and other things. It could be changes in outdoor temperature, A/C usage, or any number ...