AGM Battery Longevity
I have had my Lifeline AGM batteries for 7 years. For 2 of those years there were a lot of cycles because I was a fulltimer. I am getting ready to set out on a trip of several months and wonder if I...
Forum Discussion
I finished my capacity testing, but the results don't make much sense.
For a load I used my small 175 watt inverter to power a 60 watt light globe. I started with a full charge and a float of 13.7 volts. The only other load on the unit is the propane detector. The refrigerator and all RV lights and appliances were off. After 28 hours, the voltage had dropped to 12.2. A 60 watt bulb should pull 0.545 amps at 110 and 5.45 amps at 12 volts. That would equal 150 AH for the 28 hour testing period. My inverter was quite warm even though it has an internal cooling fan and I suspended it in the air to dissipate the heat. I don't have an efficiency rating but understand most of these units will be under 90 percent. So the testing should have used about 170 AH or 56 percent of my 300 AH battery bank. Since the batteries were only at about 50 degrees, I expected the test used at least 60 percent of capacity. The Lifeline manual indicates my voltage should have been at 12.0. The measurement at 28 hours was actually higher at 12.2. That corresponds to about 50 percent of capacity while still under load. The most accurate assessment is supposed to be a measurement after a 4 hour period without any load. It is late so I only waited 1 hour. The voltage increased to 12.5 which is consistent with batteries at 75 percent of capacity. I would love to conclude that my batteries are even much better than specs. More likely the 60 watt bulb is not actually pulling 60 watts. It seems impossible to conduct any sort of capacity testing without proper calibrated equipment.
For a load I used my small 175 watt inverter to power a 60 watt light globe. I started with a full charge and a float of 13.7 volts. The only other load on the unit is the propane detector. The refrigerator and all RV lights and appliances were off. After 28 hours, the voltage had dropped to 12.2. A 60 watt bulb should pull 0.545 amps at 110 and 5.45 amps at 12 volts. That would equal 150 AH for the 28 hour testing period. My inverter was quite warm even though it has an internal cooling fan and I suspended it in the air to dissipate the heat. I don't have an efficiency rating but understand most of these units will be under 90 percent. So the testing should have used about 170 AH or 56 percent of my 300 AH battery bank. Since the batteries were only at about 50 degrees, I expected the test used at least 60 percent of capacity. The Lifeline manual indicates my voltage should have been at 12.0. The measurement at 28 hours was actually higher at 12.2. That corresponds to about 50 percent of capacity while still under load. The most accurate assessment is supposed to be a measurement after a 4 hour period without any load. It is late so I only waited 1 hour. The voltage increased to 12.5 which is consistent with batteries at 75 percent of capacity. I would love to conclude that my batteries are even much better than specs. More likely the 60 watt bulb is not actually pulling 60 watts. It seems impossible to conduct any sort of capacity testing without proper calibrated equipment.
