Low battery voltage overnight

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iambrian asked Oct 17, '22

Low battery voltage overnight

I have a simple cheap 85Ah sealed lead-acid battery in my campervan. I am noticing that my Victron charger history is showing daily highs of 14.2v but lows of 6.5v! There is zero load shown on the controller (good, since I disconnected it!) and I can find no direct battery load (everything appears switched off) so I am assuming no load drain.

I am assuming a dead/dying battery but its 'magic eye' is a bright green which seems to suggest otherwise. The controller's battery preset is Gel Deep Discharge(2) (i.e. the factory default) - could this be performing deep discharges lowering the voltage briefly or am I correct in assuming a dead/dying battery?

I can try switching the controller off and using an ammeter to check no overnight current draw but before struggling with that I'm trying to understand the "Gel Deep Discharge" default setting.

As you can guess I'm very much a battery newbie!

battery charging

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Alexandra ♦ commented · Oct 17, 2022 at 10:56 AM

@iambrian

Do you have a direct connection or through a fuse or switch?

Check all connections between the battery and the device.

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Answer 1 · 2022-10-18T09:28:34Z

thanar answered · Oct 18, 2022 at 09:28 AM

Most probably the battery is dead. Charge it up to full, disconnect it from the system and leave it for a couple of hours. Report back with the resting voltage.

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christern commented · Dec 11, 2022 at 08:54 PM

Good idea. Even better if you first disconnect the battery and THEN charge it to full. It will make it easier to make sure there is nothing drawing or messing up any measuring.

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Answer 2 · 2022-12-11T13:53:01Z

Alexander Bartash answered · Dec 11, 2022 at 01:53 PM

Can it be the same issue as in Why did Multi RS Solar ESS discharge below the minimum SOC? ?

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Answer 3 · 2022-12-11T17:05:55Z

minmin answered · Dec 11, 2022 at 05:05 PM

85Ah lead battery is only 42.5 useable when absolute new and absolutely full.... how old is your battery? 42.5 isnt a lot depending on what youre powering and how often you can get it full.. add in a few years of age/normal use and youre down to maybe 25-30 useable.... add in some abuse.... probably even lower...

How old is the battery? mostly sounds like it is toast.
To check the resting voltage you should leave it for 24 hours at least not connected to anything after a full charge. Also could do a load test where you apply maybe 3-5A of load and see how far it gets ya...

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Answer 4 · 2022-12-11T17:16:33Z

kevgermany answered · Dec 11, 2022 at 05:16 PM

Deep discharge refers to battery type, not the behaviour of the charger. These inbuilt settings are suitable for most AGM batteries. The magic eye isn't necessarily going to tell the truth.

With such low overnight voltages, your battery will have been damaged and is useless. As @Alexandra said, check for loads you may have missed. Otherwise if you missed them the new battery will go the same way.

As a rule of thumb, don't let AGM go lower than 12.1V off load and charge asap after this.

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