Tony,
You haven't given enough information. However, let me try to explain as best I can from the information you have given. I assume when you refer to 2-6 volt batteries, you are referring to deep-cycle batteries wired in series to produce 12 volt output. With this assumption, the following results will vary with the specs of the batteries:
70 watt solar, at max. output will charge the batteries at the rate of 5.8 amps per hour. So, given 12 hours of daylight, the solar panel should be putting approx. 70 amps/per day into your batteries. If your batteries are each rated at 225 amp/hr, you have 450 amp/hrs available, but you are only charging them at the rate of 70 amps per day.
Check the rating of your batteries, and if they are rated at less than 225 amp/hr the charge ratio is better, but still not enough to fully charge them. At the rate your solar panel is charging (at max. output) it would take approx. six and one-half days with NO LOAD to recharge the batteries fully. Please understand, if the daylight is subdued, your solar panel will not operate at its maximum capacity, so the charging rate would be less. Does that make sense?
If your batteries are fully charged (by your tow vehicle) when you arrive at camp, and you use no more than 5.8 amps per hour, then your batteries will not run down. However, if the fan for your heater comes on, it is using more than 5.8 amps per hour.
The solution to your dilemma is to (1) get more solar panels to improve the charging capacity, and/or (2) buy a generator to charge the batteries. Two more solar panels would produce about 17 amp/hr charge, which may meet your needs. You mention you use minimal lights and radio, but it would appear you are draining the batteries faster than that. How many lights do you have on at one time, for example? Each lamp draws at least 1.5 amps, or more.
I hope this helps you chose the right solution to give you the camping enjoyment you desire.
|