Charging issue

[cfish]

Been driving my m1009 a bit lately. Charge on the voltmeter usually top of the yellow when first started and after a minute usually works its way to 3/4 top of green arc. Last weekend drove it at night with heater and lights on and after a short while volt gauge down into the yellow. Drew my batteries down by the time I made it to my house. Took both batteries today to auto parts and one was dead. Replaced the bad battery and started the cucv. Volt gauge still in yellow. Other battery was not charged and currently have it on charge. I know it requires enough voltage to excite the alternator. With the one good battery and one discharged could I still have a problem of not exciting one of the alternators? Both alternators putting out current around 14-15 volts. Or should I check for a grounding issue. All the cables are good and clean and fairly new.
Thanks

 

[cfish]

I miss spoke the alternator on the discharged battery was reading 12.4 can't read my own notes.

 

[trooper632]

What was the diagnosis of the problem

 

[87cr250r]

A 100 amp alternator will take about 45 minutes to fully charge a dead battery.

I would start your diagnostics first by fully charging your batteries, 12.6 volts. Put them in the truck and start it. They should immediately jump to 14+ volts if the alternators are working.

If the batteries are anything less than 12.6 volts then you're going to have to wait for them to charge to get the full picture on the alternator condition.