Returning from a trip yesterday we stopped at a rest area for lunch. I turned the inverter on and voltage was 13.75. Within 15 or so minutes voltage had dropped to 12.0. At that point I turned it off. Earlier in the week I turned it on and voltage warning came on within a few minutes @ 10.0 volts. According to mechanic, specific gravity was good on all batteries. I'm not sure if I believe that but lets go with it for now.

If batteries are good, how do I test the inverter? (Prosine 2000 watt model)
If I have to replace inverter what would you recommend?

If battery/ies are bad should I replace all or only bad one? (Current batteries {coach and chassis} are 5 years old)
If I have to replace batteries what would you recommend?

Thanks, Steve

Hi
Gerald will probably weigh in on this with a better opinion.  Until then here is what I know.
Have a draw test on your batteries, they may read good static, but not hold up under stress.
Check your connections very closely.  I took ours apart and checked the cables, connections and cleaned all the above.  I still missed a bad ground on one.
I am assuming that the charging system is a steady 13.7V.
I have been repeatedly told by professionals that a MH battery life is about four years.  I replaced them all and that solved most of the problem.
One thing that did help was making sure that the inverter / charger was set to wet (lead acid) not gell batteries as there seems to be a difference in the float charge and cycling.

Good luck
Keith

Your problem sounds like you either have a bad connection or bad house batteries, but their are several questions that need to be answered. First how many amps were you drawing from the batteries to make them drop from 13.7V to 12.0V in 15 minutes? Second have you serviced your house batteries (cleaned all connections and filled with distilled water)? Third have you load tested your house batteries? With the answers to these questions, we can determine the cause of your problem.

If you have one or more bad house batteries, the question of how many batteries to replace is hard to answer. Normally it is recommended to replace all house batteries at the same time, but if a load test shows that you have only one bad battery, there can be a very strong argument to replace only the bad battery. If you are planning to keep the coach at least 3 or 4 years longer, and the house batteries are four years old now, I would replace all 4 house batteries with a good lead/acid golf cart battery like Trojan.

If you have a need for higher battery capacity like running a CPAP machine at night, or if you are very poor a battery maintenance you may want to consider replacing your house batteries with AGM batteries, but they will cost about twice as much as a good wet cell battery.

Gerald