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nealies avatar image
nealies asked

Voltage drop and mid-point voltage deviation spike on AGM

Hi all

Newbie here, first post and I'm not v technical - please be kind!

I have 2 x Trojan AGM 200Ah 6v batteries connected in series that have been well maintained, they are 14 months old. 4 days we saw our inverter had switched off overnight. When we checked the Victron app the voltage had plummeted in the early hours, and simultaneously the mid-point voltage deviation had rocketed, the system then returned to normal after approx. 2 hrs (and we manually restarted the inverter) – screen shots below. The situation has occurred again early this morning, screen shots also attached. Please would someone be able to advise what our issue may be?

Many thanks in advance

Laurie Voltage_Mid Point 041022.jpgCurrent_Mid Point 011022.jpgVoltage_Mid Point 041022.jpgCurrent_Mid Point 041022.jpg

battery system voltage
voltage-mid-point-041022.jpg (65.4 KiB)
current-mid-point-011022.jpg (78.6 KiB)
voltage-mid-point-041022.jpg (65.4 KiB)
current-mid-point-041022.jpg (64.4 KiB)
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1 Answer
ludo avatar image
ludo answered ·

One dead cell.


Check the acid-level on all cells (if possible) , you might have to remove the lid under the label.


You should still have warranty on those batteries, I guess you will need new ones.


Btw, do you have a balancer installed ?


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christern avatar image christern commented ·
I haven't heard about AGMs that can be checked acid level on. AGM means, as far as I know, Absorbed Glass Matt where the acid is absorbed in a matt and not fluid.

Disconnect the batteries and charge them separately and wait for 24 hours and check voltage and you will see if one cell is dead. If so that battery will have a lower voltage.

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ludo avatar image ludo christern commented ·
"if possible", normally there are screwtops under a plastic cover under the label. At production the acid has to get into the battery.


Don't touch if it's possible to get warranty ( I never did get).




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