1. Is it normal for one of these cars to kill a battery from sitting without being driven in 1 month?

2. What would cause the fuel level gauge to act erratically?

The car is my uncle's and he had it to the dealer to troubleshoot an electrical problem and since then these two other problems have appeared. The dealership says the battery dying is normal and that he is lucky that it even lasts that long. Any help would be appreciated.

Of course the battery dying in a month is not common but depends on the condition & age of the battery. I've seen cars left at our shop for 6 months still start w/o jump! And others 4-6 weeks and there dead.
Most erratic gauges are from defective sending units!

I had a battery drain that was traced to a faulty aftermarket alarm system. If anything has been added to the circuitry you may want to start the trouble-shooting there.