Question: I have a 1997 Coachmen Catalina Sport. Everything that runs on 12-volt makes the battery low. I have to start the engine for a while and it charges, but in a little while I have to do it all over again. I’ve had the battery checked and was told it’s okay.
Answer: Without more detail it is difficult to give a simple or specific answer, but here are a few thoughts and speculations on the subject.
Just because your battery tests OK, it does not mean that it is OK for the power demands you place on it. From you description of the problem and how you recharge the battery, I suspect that the battery is not being fully charged before you start drawing power again.
If the battery is in fact good, then it must be that the power demands you are placing on it are too great for that battery. So many things can affect the usable energy stored in a battery that it is not possible to explore all the reasons. But perhaps some of this will point you in the right direction.
Possible problem 1: Battery not good:
Since you are running your engine and using your alternator to charge your battery I can only speculate that you are not running the engine long enough and that the battery is only being partially charged. I also have to speculate that you are using the 12-Volt appliances because you are not plugged into power.
The engine and alternator must run at a fast idle and for as long as it takes to cover the equivalent of twenty to thirty miles for the battery to be fully charged, and much longer if the battery is a deep cycle battery. What you seem to be doing is only giving the battery what is called a surface charge. This surface charge only lasts a few minutes and the battery soon starts to deplete its power reserves.
If you do this long enough the battery will become sulfated and its useful life will be shorter and shorter with each partial charge. In the end you will not be able to recharge the battery and you will have to replace it.
You said the battery tested OK but how far did you drive to have the battery tested? If you drove more than thirty miles, you may have recharged that battery sufficiently to have it test OK. Did the shop do a load test on the battery? Did they test each cell to make sure the battery did not have a dead cell? All food for thought. You may need to get a new battery.
Possible problem 2: Charging System not working correctly
If you are plugged into power and the 12-Volt appliances are running your battery down, then you have a charging system problem. More specifically, the charger that is supposed to charge your house battery while you are plugged into power is not operating properly. You should probably go to a qualified RV shop that specializes in RV electrical systems.
Possible problem 3: Battery not adequate for power needs
The other possibility is that the battery is not capable of providing all of the power you need or for as long as you need it. You need to check the battery’s load capacity to see how it compares to the power requirements placed on it. If you have not already done so, I suggest that you make a list of each of the 12-Volt appliances that run off your battery while the engine is off. Then calculate how much each appliance draws on an hourly basis in AMPS.
Determine how many hours you expect to use each appliance. Once you have all this data you can calculate how many total AMP hours are required for your needs. The number of AMP hours calculated will allow you to determine if your battery has sufficient Reserve Capacity (RC) to accommodate all of the power requirements.
The solution may be as complex as redesigning your 12-Volt system to accommodate more/bigger batteries or as simple as just managing your power needs to match the battery’s power capacity.
P.S. Just FYI in case you are using a car battery: Car batteries, also called starter batteries, are rated in Cold Cranking AMPS (CCA) and do not have sufficient reserve capacity to run 12-Volt appliances for very long. This could be your problem.
Hope this helps. Other comments welcome.