Originally Posted by KarenW
We just finished a week camping with full shore power hook up and at the end of the week when I thought to check the battery power it was down to 12.1. I was surprised as it was 13.1 at the beginning of the week and we were plugged in the entire time. What could be drawing down the batteries?
Generally speaking, all the wires that power 12 volt outlets/devices and the wires to the battery are connected together at the power center. When you're plugged in to shore power the power center supplies 120 volts to outlets and 120v devices like the refrigerator. The power center also has a 120v to 12v converter that provides 12v to the 12v outlets/devices and for battery charging (assuming the main battery switch that connects the batteries to the power center is ON).
So if you're measuring your battery voltage when you're plugged in to shore power, you're actually measuring the 13+ volts the power center's converter is supplying to the batteries and 12v outlets/devices. You can see the difference if you unplug briefly from shore power and check the voltage again. You'll then be measuring only the battery voltage which will be significantly lower than when plugged in to shore power. (Battery charging voltage from the converter has to be 13+ volts in order to be able to charge the battery.)
According to your report, the battery was down to 12.1 volts after a week of being plugged into shore power. That IS unusual because after a week of charging the battery should be fully charged, somewhere between 12.6 and 12.9 volts, depending on the type of lead acid battery you're using.
There are several things to check. The first is to see if the power center 120-12v converter is working. Turn off the main battery switch to take the battery out of the circuit. All the 12v outlets/devices will be off since there's no power to them. Then plug in to shore power. If the converter is working, the 12v outlets/devices should now work as they are powered by the converter which in turn is powered by the 120v shore power. OK so far?
Then check to see that the battery is being charged. While the main battery switch is still off (which disconnects the battery from everything) check the battery voltage at the battery + and - terminals with your little multimeter. It should be be somewhere between 12.1 and 12.9 volts, depending on its state of charge. The turn the main battery switch ON and plug in to shore power. The converter in the power center should now be charging the battery. To check, use your multimeter again at the battery terminals. The voltage reading should be significantly higher, probably over 13 volts. If the battery voltage doesn't change when connecting the converter, that tells you there's a break in the circuit somewhere between the converter in the power center and the battery. Double-check that the main battery switch is ON. If the battery still isn't charging, the most likely cause is that a fuse in the wiring between the power center and the battery has blown. The fuses are located near the battery.
After doing all this, if you're still having problems, report back with what you did and what voltages you observed. It's possible the battery is dying or there is some other problem, but usually doing what's described above solves the mystery.