never had 2 batteries before...probley somethin simple,but...454,almost 250,000 runs like a dream.Expet for gas milage,and the bateries

 

Have you checked the alternator? How are the batteries connected?

 

check connections, check condition of both batteries. a failed battery will suck up as much voltage as an alternator can feed it, giving the impression that a no charge situation is occuring. good luck, keep us posted

 

I would disconnect one of the batteries and while they are not connected together, measure the voltage across the terminals of each battery. Should be around 13.2 volts for a fully charged battery.
Then connect one of the batteries up and start the engine. Measure the voltage across the connected battery. Should be around 14.4v for a properly operating alternator.
Repeat that with the other battery connected. If one of the charging voltages is lower than the other, it means that battery is loading the alternator more and may have a shorted cell.
To check the capacity of each battery, connect one battery at a time, put your meter across the connected battery's terminal and hit the starter. The voltage should not drop below 10v. Do that with the other battery connected and if one drops much more than the other, you have a weak battery.
Since the batteries are connected in parallel, you have to isolate them to see which one is bad. if I found one bad and they were about the same age, I would replace them both anyway. Good luck.

Or you could take it to Auto Zone and let them do it for you for free.