Toyota Repair: Toyota 4 Runner Battery Charging, dual batteries, toyota 4 runner

Question
Hi Mike,
I have a 93 2.4D Toyota 4 Runner with dual batteries.   The batteries keep going flat and after charging all night they run for the day and are flat again the next morning.   How do I tell if it's the batteries or the alternator?
Cheers Steve

Answer
Steve,
You cant check the charging system unless your batteries are charged. You need voltage to make voltage.
Checking the charging system on a dead battery wont be acurate even if its running.
So....Charge the batteries again and check the voltage when its running.
Normal charging system voltage is about 12.8- 14.2.
If you dont have access to a battery tester, and the charging system is in spec. replace the batteries.

Mike