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Old 03-07-2020, 09:55 AM   #1
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Will I overcharge my new AGM's?

I just put two new AGM deep cycle batteries in our fifth wheel; two Group 27 12V in parallel. I'm new to AGM. I've seen information that says AGM batteries can be ruined by overcharging. We are leaving on a 1,870 mile tow from MN to Tucson in a couple of weeks. That's a lot of hours on the road with the truck pumping out 14.4 volts. Is there any chance of damaging the batteries by that many hours of charging from the truck?
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Old 03-07-2020, 11:53 AM   #2
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No- the amount of amps being sent from TV to your batteries will be minimal.
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Old 03-07-2020, 12:04 PM   #3
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I just put two new AGM deep cycle batteries in our fifth wheel; two Group 27 12V in parallel. I'm new to AGM. I've seen information that says AGM batteries can be ruined by overcharging. We are leaving on a 1,870 mile tow from MN to Tucson in a couple of weeks. That's a lot of hours on the road with the truck pumping out 14.4 volts. Is there any chance of damaging the batteries by that many hours of charging from the truck?
If it's not damaging your truck battery I can't see it damaging your you trailer. 14.4 volts seems to be well within the recommended charging range suggested by most AGM manufacturers.

FWIW, just for the heck of it take a voltage reading at your trailer batteries while connected to the truck and engine running. The wire size in the truck is usually small and the distance from alternator causes a significant voltage drop while batteries are charging. In a way this is protecting the batteries from over-charging. The downside is that this also limits charging current when it's needed most, when batteries are discharged.
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Old 03-07-2020, 12:48 PM   #4
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Thanks for the responses. I do have a Victron monitor. So, when I get hooked up I'll look at the voltage. I'll also be able to see the amperage being pushed by the truck. Maybe I'm over-thinking this situation.
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Old 03-07-2020, 01:13 PM   #5
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AGM's like to be charged at a higher voltage, 14.6-14.8 volts. I even leave my CTEK smart charger in 'winter' mode, which charges at that higher voltage. Although the preferred float charge for these batteries is 13.2-13.8 volts, I doubt your TV's output for the limited hours you are driving (I assume there will be plenty of breaks in between drives) would be detrimental.
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Old 03-07-2020, 01:22 PM   #6
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Owning a voltmeter that graphs for me. I can assure you unless the wiring has been extensively modified you are in no danger.

The wire from the tv to the rv is so long the voltage likely will not exceed 13 volts. I have a 220 amp alternator. But the wire back to the rv batteries is LONG!
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Old 03-07-2020, 03:44 PM   #7
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I just put two new AGM deep cycle batteries in our fifth wheel; two Group 27 12V in parallel. I'm new to AGM. I've seen information that says AGM batteries can be ruined by overcharging. We are leaving on a 1,870 mile tow from MN to Tucson in a couple of weeks. That's a lot of hours on the road with the truck pumping out 14.4 volts. Is there any chance of damaging the batteries by that many hours of charging from the truck?
That's what the 'voltage regulator' is for. Unless there is a *'weak' cell in one of the batteries, the regulator will take care of it. * Weak cells-batteries, never charge fully, keep calling for more charge, causing heating-boiling of the cells.

Happy Trails!!! Be Safe out there!
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Old 03-07-2020, 03:48 PM   #8
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Thanks everyone . . .
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Old 03-07-2020, 05:29 PM   #9
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I would say your probably ok--- In most cases unless your starting Battery and RV batteries are isolated from each other, the Starting Battery in your tow vehicle will probably come up to the max voltage that your Alternator regulator is set up for. As soon as the regulator of the alternator "see's the higher voltage it basically shuts down output until the Min. voltage is met and the whole cycle starts again Your RV Batteries would take longer to come up than your TV start Batteries. In essence, the deciding factor will always be your TV Starting batteries if they are not isolated from each other thru a dual charging module .
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Old 03-07-2020, 07:33 PM   #10
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As others have written, no worries. The voltage regulator will take care of your concerns.
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Old 03-07-2020, 07:57 PM   #11
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Page 19 of the Lifeline technical manual lists charge voltages for it's AGM batteries. Other AGMs will be similar

https://lifelinebatteries.com/wp-con...al-5-06-19.pdf
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Old 03-08-2020, 09:24 PM   #12
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This makes me wonder if my WFCO converter would ever charge at a high enough rate for an AGM battery. I can only get 14 volts out of my truck with the headlights on. Im sure there is a significant voltage drop at the camper battery when charging from the truck. Jay
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Old 03-09-2020, 06:54 PM   #13
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This makes me wonder if my WFCO converter would ever charge at a high enough rate for an AGM battery. I can only get 14 volts out of my truck with the headlights on. Im sure there is a significant voltage drop at the camper battery when charging from the truck. Jay
There is quite a lot of information on internet about AGMs; strengths, weaknesses; how to charge. And, of course, some of it is contradictory . . .
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