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01-19-2025, 03:17 AM
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#1
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Junior Member
Join Date: Sep 2024
Posts: 6
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AGM how low is to low?
All,
I recently purchased a new Dazzle Class B rv. It has 2 100ah AGM batteries installed. I’m noticing that when I run the heater and tank heaters at night that the voltage level indicators for the batteries will show the yellow caution flag for low voltage. I caught this in the middle of the night while camping in 25 degree temps. I setup the auto start feature on the genny to start up around 11.8 volts if I remember right.
It will also show that if I’m only running the furnace but less frequently.
With the furnace and tank heaters on it will start the genny multiple times overnight to recharge the batteries. I have it set to only run for an hour each time.
What is the safe minimum voltage for AGM batteries? To me, they don’t seem to keep their charge for very long compared to Lifepo4. I had a toy hauler that I setup with 200 amps of Lithium and I never came close to that kind of voltage drop at night. But, I also didn’t have tank heaters in the toy hauler. Just a furnace.
I’m contemplating converting to lithium batteries but I don’t want to void any warranty on anything.
At what voltage level will the AGM batteries become damaged?
Thanks..
Don.
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01-19-2025, 07:34 AM
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#2
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Senior Member
Join Date: Jul 2014
Posts: 37,095
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When you hit 11.8 volts with the tank heaters or anything else running, that's not an accurate reading.
Checking a batteries state of charge under load doesn't work. The battery need all loads removed and sit for 2 to 3 hours before a voltage reading, for capacity, can be made.
Reset your AGS for 11 volts and see how it works out, a full discharged battery is 10.6 resting volts.
A better solution is a battery monitor, it's like a gas gauge for your batteries.
As far as recharging, if your discharging to 50%, that's 100 AH. With a 50 amp charger, it will take a minimum 2.5 hours to get them recharged near full.
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01-19-2025, 10:38 AM
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#3
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Senior Member
Ford Super Duty Owner Outdoors RV Owners Club Jayco Owners Club
Join Date: Jun 2018
Location: Auburn, WA
Posts: 809
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Quote:
Originally Posted by D308
All,
I recently purchased a new Dazzle Class B rv. It has 2 100ah AGM batteries installed. I’m noticing that when I run the heater and tank heaters at night that the voltage level indicators for the batteries will show the yellow caution flag for low voltage. I caught this in the middle of the night while camping in 25 degree temps. I setup the auto start feature on the genny to start up around 11.8 volts if I remember right.
It will also show that if I’m only running the furnace but less frequently.
With the furnace and tank heaters on it will start the genny multiple times overnight to recharge the batteries. I have it set to only run for an hour each time.
What is the safe minimum voltage for AGM batteries? To me, they don’t seem to keep their charge for very long compared to Lifepo4. I had a toy hauler that I setup with 200 amps of Lithium and I never came close to that kind of voltage drop at night. But, I also didn’t have tank heaters in the toy hauler. Just a furnace.
I’m contemplating converting to lithium batteries but I don’t want to void any warranty on anything.
At what voltage level will the AGM batteries become damaged?
Thanks..
Don.
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Bear in mind that the lithium batteries maintain a higher voltage under load over a longer period of discharge than FLA or AGM. You can see on the voltage chart below that they remain well above 12v until nearly discharged. That would explain the difference in behavior that you've observed between the two campers.
__________________
TT: 2019 ORV Timber Ridge 23DBS, Blue Ox SwayPro 15K/1500
TV: 2019 Ford F-250 XLT SuperCab LB, 6.2L, 4.30/e-locker, 4x4, 164" WB, RoadActive Suspension
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01-19-2025, 11:39 AM
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#4
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Senior Member
Join Date: Nov 2018
Location: Beaver Dam, Wisconsin
Posts: 5,904
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The biggest difference between the two campers is most likely the load being consumed. Those tank heaters use a lot of power.
I had 12 volt tank heaters in my Kodiak Cub. I quickly found out that 12 volt tank heaters were not practical with only 200 amp hours of AGM batteries.
I sealed and insulated the belly area and heated it all using a duct from the propane furnace. Results were much better.
Battery charging
Lead acid batteries typically require 14 hours or more for a full charge. 4 hours with a good quality charger may get an 80% state of charge. 1 hour gets next to no charge.
Good advice posted above about using a current measuring (Coulomb Counter) system for starting the generator. Heavily loaded lead acid batteries are not going to present good data using voltage alone.
__________________
Paul Bristol
Kodiak Cub 176RD
Nissan Pathfinder 2015
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01-19-2025, 01:13 PM
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#5
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Junior Member
Join Date: Sep 2024
Posts: 6
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Thank You
Thanks to everyone for the advice.
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