Re: AGM batteries - voltage falling


I do think it is a battery problem . Looks like they don’t keep the charge . 

Envoyé de mon iPhone

Le 28 mai 2022 à 09:04, Jose Alegria <Josealegr@...> a écrit :

New developments:

The Mastervolt dealers comes and the batteries are tested after 20 hours of shhore power on with 60 Amp charger  and the results are bellow:


5 batteries with > 80 % and 3 batteries with 73,76 and 77%

The technician  don’t find any problem with installation, and any batterie at shortcut; the charger parameters are correct, reviewed all equipments .


Last night at 22,32 with 60 Amp charger ON the values was:

Then I  disconnect the 60 Amp charger and at 22:35 the values was:


The consumption are regular during the night : if my battery bank was actually ± 80% of 640 Amp I have ± 500 Amp — If the statues of charge goes down 9% ( from 100% to 91% )  I use ± 45 Amp during all night

Today 9 hours later after some sun light the values was: 

But early in the morning the voltage fall down t o 21,20 V and the freezer and fridge stop work again.


Ideas ?

Thank you for your support
Attachments area

José Alegria
Mobile: + 351 91 866 30 37

On Fri, 27 May 2022 at 15:48, Dean Gillies <stella@...> wrote:
The default behaviour of your charge algorithm (for the 6 months your batteries were being charged by Solar and shore chargers) is as follows:

1. The maximum absorption time would be 1 hour (since the batteries would be at float voltage overnight).
2. The tail current would be 2A. 

As Alan indicated, the bulk stage each day would be almost non-existent since the voltage would rise very quickly from float to 28.8V, and would hold this voltage until either the current dropped to less than 2A (I believe that's the total of all 3 networked MPPT's, does anyone know for sure?) or a period of 1 hour elapsed. This does not seem like enough time at higher voltage to badly damage a battery bank over winter.

This does not eliminate overcharging completely, but in theory it should not be caused by the solar operating properly according to your settings.

Let's see if the technician detects a failed cell before we postulate further causes of the failed bank. Fingers crossed you can get some warranty assistance from Mastervolt.

Alan's comments about balancing are excellent for future consideration if you stick with lead batteries.



Dean Gillies
SV Stella *****,  Amel 54-154

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