If you run on batteries a lot then you need to know what's going on with the charge/discharge cycles. Unfortunately it's not as simple as measuring the voltage or the amps.
Our other fiberglass camper is a boat. We have spent six months living aboard down in the Bahamas where we never plugged in. We have a single 120 watt solar panel
but run the diesel engine daily to recover our 50 to 70 amp hour short-fall. Mainly we run short because we run the fridge
24/7 and with the solar panel
in the dark ...
Anyway, we use a Xantrex TM500 (now called the TM500A) to measure our 220 amp hour gel cell house bank. While it gives a digital readout of voltage and amps, it accumulates the net gozinta/gozouta amp hours between charging cycles. We can see what we've used since we last ran the engine (net of the solar
panel) and also see how much we've replaced while running the engine. We can also see what we're getting from the solar panel
or what any given appliance is using (at that moment) by manipulating the circuit breakers.
We also run a Xantrex 1800 watt inverter that has a digital voltage display. Both the monitor and the inverter are directly feeding from the batteries on very heavy and short runs of wire yet they report different voltages. Usually the monitor reports a tenth or two under the voltage reported by the inverter. Also we have a GPS mounted on thin wire probably 20 feet from the batteries and it reports the highest voltage of the three by a tenth of a volt.(that's odd you'd think it would be the opposite). Checking these against my Fluke meter reading at the batteries reveals the monitor voltage to be the most accurate. But then it's also the most expensive instrument too.
As mentioned previously, conservation is the key. We keep the fridge
as full as possible, even filling empty space with water jugs. (I know beer would work better) LED and fluorescent lights
help a lot. What seems to hurt us the most after the fridge, is whether we watch a DVD on the TV in the evening or whether we use the HF/SSB radio in broadcast mode much. When sailing, the killers are the autopilot and radar. Even when sailing, we often end up running the engine just to keep up with power demands.
We're all electric on the Scamp
too but we always plug-in when camped. I'd go solar
on the camper except that being Florida campers, we prefer to park in the shade.