Charging a AGM Battery

Last week I forgot to Turn of my chassis battery switch. Yesterday I went to check on something in the motor home and the steps would not come out. Nor would the Motor Home start. The chassis (Starter Battery) was dead. I had left the radio and a couple of other things on. Normally I disconnect the battery using the Chassis disconnect switch by the door when I am not going to be using the Motor Home or when it is stored. Senior Moment I guess. I thought no problem I will get the Battery Charger and recharge the battery. Little did I know what I was in for. I hooked up the battery charger and it kept cycling on and off. I checked the terminals and they were clean and the charger was hooked to the correct polarity. Hmm What to do. the battery was almost dead. The battery charger needs 10.5 volts to run. This is a safety feature of the battery charger. Oh well I will use my 10 amp trickle charger. same thing with it. So I decided to remove the battery and bench test and charge it. (what a job). The battery sits way down to the left of and between the radiator and grill, (see Picture below). 

 

The battery weighs 50 Lbs. I had to bend over the opening and reach way down to unhook the battery using a 10 MM and 6 MM socket and end wrench. I got it all loose and now the hard part getting it out. I bent over the opening with the hood up and started to lift the battery out. It was awkward and heavy, I was barely able to get it up to the lip of the opening, and had to tip it on its side. It was a good thing that it is a sealed AGM battery (which I did not know at the time). After getting it out, that was when I noticed that my right arm was bleeding. The metal fins of the grill just inside the lip opening had cut the inside of my right arm from my elbow to arm pit. (see picture below of fins.

The red arrow shows the metal fins. I doctored my arm and cleaned the cuts and applied some disinfectant. Got the battery on the bench and discovered that it was a AGM Battery. I did not have a AGM Battery Charger and none of the 3 battery chargers would start because the voltage in the battery was almost dead. So I did some reading about AGM batteries. There are 3 methods of charging a Dead AGM Battery when you don’t have a AGM Charger. I will only cover the one that I used.

I took a set of battery cables and hooked to a good wet cell lead acid car battery in my jeep and hooked the other end to the AGM battery making sure pos to pos and neg to neg. I then took my 10 amp automatic battery charger and hooked it to the agm battery. I Left this setup for one hour checking to make sure the battery or the cables were not getting to hot to touch. The voltage from the jeep battery tricked the battery charger in to running because it could see 10.5 volts or more. After an hour I checked the voltage of the AGM Battery, with everything unhooked, making sure I had the 10.5 volts so the charger would work without the jeep battery. I continued charging the AGM Battery until I had at least 12 volts. I checked the wires and the battery to make sure it was not getting to hot to touch. This in case there was a internal short which if badly overheated could cause the battery to explode. I then installed the battery in the motor home and started it up to finish charging it. I did use a piece of carpet over the lip when reinstalling the battery. I learned a couple of lessons today. I also wonder how many people have replaced a AGM battery because they could not get it to charge after being run down.

Mel

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Author: Mel

I am a Retired PC Tech. I love to travel in a Motor Home with my Wife. I am a avid RVer and like to camp and travel. I am a commercial Pilot and hold a Novell Education certificate in Networking configuration and installation. I like to read and like country and western Music.

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