Battery issue maybe.

[bennydog]

Could be me but this does not seem right. I reinstalled the 2 12 volt batteries over the weekend. They had been in the garage on a bench(not on concrete floor) hooked up to a battery tender. Over the winter I had purchased a 12 volt meter called a volt minder from universal power group. ( I give up on the link thingy)I've wanted to be able to watch the batteries more closely than the indications on the tank panel. So I plugged this thing in and it tells me the batteries are at 12.5 volts. When I hooked the trailer to shore power the meter reads 13.67 which I'm guessing is the output of the converter. I'm thinking that the batteries were not fully charged when I installed them so I let the whole thing sit overnight. When I unplug shore power they now about 12.97 volts. The Volt minder has an alarm function to alert you if the voltage ever drops below a point that I can set. They recommend that it be set at 12.1 volts. I was testing the furnace with shore power disconnected and the 5 minute run of the furnace would drop the voltage down to 11.6, of course the alarm went off at 12.1. With nothing running in the trailer the voltage would after about 20 minutes climb back to 12.6 volts. Here are the questions, should the battery voltage drop that much that quickly or do I have a problem? They are interstate batteries and they are 8 months old. Why would the voltage drop so low and then slowly climb back up?

[Flyguy]

The battery voltage will normally drop when a load is put on them and the furnace fan is one of the worst current draws of them all, it will suck a battery down in a hurry. Batteries will normally recover some after a high load is cut off, this is normal and all lead-acid types seem to have this trait. You can think of it this way: each device draws a certain power and that's calculated by the formula P = I X E (where I =s current in amps and E =s Voltage), if the voltage goes down the current must increase because the device will maintain the power in watts no matter what, you can burn up a motor if the voltage drops low enough. I'm not sure what the technical reason is for the battery kick back in voltage but it does happen. Hope my rambling explanation is of help