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AGM 8D battery question

Yahoo Message Number: 81103
My monitor will show 13.2 to 13.4 as my charge on my batteries when I'm plugged in to shore power but the charge drops to 12.6-12-8 after I disconnect and am running off the inverter. I have a domestic refer which runs while I'm on the road but not much else. Is this drop in voltage normal for AGM 8D domestic deep cycle batteries? These are house batteries not engine cranking batteries.

Thanks

Chuck

Allure 470
31695

Re: AGM 8D battery question

Reply #2 –
Yahoo Message Number: 81106
Chuck - The quick answer is yes.

Our lead acid batteries are comprised of 6 individual cells connected in series. Each cell has a VOC (voltage open circuit) of 2.1 VDC @ room temperature with no load. That adds to 12.6 VDC at the battery terminals and is a pretty standard VOC for this type of battery. As current is drawn that voltage will degrade based on amperage, battery condition, state of charge and temperature. On AGM batteries the no load voltage (after a battery has stabilized) can be used to determine its SOC (state of charge). You can't measure specific gravity of the electrolyte on AGM batteries. Each manufacturer has a SOC table that reflects their battery design. You might see 12.3 VDC equate to 50% discharge, for example.
A fully charged battery (SOC = 12.6 VDC = 100%) can be floated indefinitely without changing its SOC. Common voltages are 13.2 - 13.6 VDC depending on temperature, chemistry and other design parameters. Smart chargers will replace amps removed from the battery to maintain this float voltage. A reading of battery amps would show 0 (or close to it as a slight trickle amperage) in this case. Some chargers will float for a while then shut down with a "Battery Full" message. When battery voltage drops they will resume a float charge and so on.
The goal of a charging system is to not stress the battery or boil off electrolyte (referred to as gassing). If your house bank is supplying significant amperage (invertor load) and still maintaining 12.6 - 12.8 VDC I'd say you're doing well. Proper charging comes first followed by responsible discharging. One needs to keep track of relevant battery/charger parameters. This is a complex subject with many details and variables. I hope this basic treatment of the subject has been helpful.

At 04:28 PM 7/24/2012, you wrote:
 

Re: AGM 8D battery question

Reply #3 –
Yahoo Message Number: 81115
Chuck,

As others have pointed out, that's normal. If you have Lifelines, this is the SOC parameters in general terms:

100% - 12.8
75% - 12.5
50% - 12.2
25% - 11.9
0% - 11.6

Tom

Lifeline Batteries
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