I have a clock radio/stereo that runs off the battery.  Other than that, its only the occasional pump use (I turn off the pump when not in use), and extremely conservative use of the internal lights.

I don't have a gage or anything.  All that I have is a red light that shows when the solar charger is charging.   

Hillview,

Have you tried going back to the place that installed your solar and telling them it's not working for you?

How did they calculate the size of panel and type of battery to install?

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What is your panel rated at? I have a 75w solar setup at a remote horse camp. Keeps 4 deepcycle batteries topped of. When i get there they are hot! It works great. Batteries last longer also. It wrecks them when you let them go dead.You can tell if it is working by measuring the voltage. Does it charge the battery back up in time? Clock radio stereo?Is it 12 volt?Is an inverter being used?Solar panels won't run much on themselves (unless you have lots) they just fill your STORAGE BATTERY for later use. The more batteries the more power stored.What is the condition of your batteries?

I'm just guessing here but I think you are relying on the solor panel to much. If you have an 75ish watt panel it will put out about 4ish amps only when the sun is directly overhead (out of the shade)! You might get a full 4ish amps between 10:30 am  till 2:30pm it is much lower the rest of the time and of course at night it is nill. If you can keep it perpindicular to the sun of course your maximum wattage duration will be longer. That is not much! But it will supply a battery with enough to keep it charged and ready to go. Most Inverters draw current when pluged into the 12v even if you don't use the 110V, only plug it in when you need it. My 300w inverter will draw 5-8ish amps 12v when in use running a laptop. An hour or two of that with the lights (Interior lights draw more than you think), and clock on will get rid of that days charge. The clock radio is a constant drain. Not a lot just telling the time but listen to the radio and it may draw 1-1.5amps depending on the volume level or playing a tape. I bet the solor panel is working for you. It seems like for the price we pay it should solve all our problems! You can buy a cheaper 1000w generator for what an installed 85w system with controller costs. If you can monitor the voltage of your batteries you can tell when you are using it to much. Another battery will help alot also. I would depend on the solor panel more to keep your batteries alive through the winter. I hate trashing good batteries! The worst thing you can do is let them set and discharge! Oh! How old is the battery? Is it very old? Has it ever gone dead? Is it a deep cycle? Ok Hillview I'm not an expert but you just got my $.02's worth I hope it helps!

It should be easy to install the 2nd battery it sounds like it is already set up for it. Just make sure the +goes to+ and the - goes to -. You may have to make up some 10gage jumpers to connect the two batteries. Lean on the dealer nicely and i bet they can make a set for you. 

Your 2 cents makes sense.  Come to think of it, I had my fridge running on LP.  I think that draws some power too.

 The dealer isn't very close so I was going to install the second battery myself.  All I have to do is connect the two positives and two negatives together?  Any special isolators, bells, whistles, or switches needed?