Joy, you can find an inexpensive multimeter at Harbor Freight which will provide JUST about the same results as a more expensive unit. Instructions are included for checking batteries. As far as your water heater you should do an internet search for your water heater for parts. If the water heater is an Atwood, the company has two different heating elements. One element screws in and the other bolts onto the heater tank. I have made repairs to an Atwood on two occasions and the screw in heating element is not hard to service, and since your water heater is inside a storage bench it should be easy to access. All power should be disconnected before working on the water heater.