[prairieschooner]

good one Forest!
I have an inexpensive Load Tester that does a good job of testing Flooded Lead Acid Batteries, I think that I bought mine about 25-30 years ago. Harbor Freight sells one similar to mine, it uses a Heater Element to Simulate a Load;
http://www.harborfreight.com/100-amp...ter-90636.html
still a good shop that sells Batteries has a much different way to test the Batteries.
Looks like a Tester that will properly test an AGM Battery runs between about $100 to $700. Maybe a drill isn't such a bad idea?

I had a second though for Jennifer. If your Batteries have gone bad in just one year there is a problem somewhere. Extreme Temperatures could effect the lifespan of a DC Battery but you may want to have that shop test the Charging Systems. If the Charging Voltages aren't matched to the type of Battery this could effect the Lifespan. When you have them check the Shore Power Charging System (typical Battery Charger, Charging Function of the Power Inverter) don't forget to have the Alternator checked as well.