Dennis,
I replaced my original Interstate house batteries at 7 years of age because they were not holding a charge quite as long as I thought that they should when I was dry camped. I replaced them with Trojan T105 batteries because I could get a better price on Trojans, and Trojans have as good a reputation or better than Interstate does, although my original Interstates gave me excellent service.
As Larry stated in the earlier post Costco or Sam's Club will have golf cart batteries (house) about 30% cheaper than you can find Trojan or Interstate batteries for, and if you plan on keeping the coach 3 or 4 years they may be the best deal. However if you are hoping for 7 or 8 years of service I would buy Trojans. There is a good reason that over 90% of the major golf courses use Trojan batteries in their carts.
One other thing to remember, if you want to get the maximum life from your house batteries, don't ever let the electrolyte (water) get below the top of the plates, and don't run the batteries down below 40% charge (12V), OR 50% charge (12.1V) is even better.
The sealed AGM batteries are better than lead/acid batteries (Trojan) because there is no out-gassing to cause cable corrosion, have a little higher capacity, and there is no water to add, but they will cost twice as much or more to purchase.
Gerald
