Batteries charged to 80% yet volts dropping to 11.3 ?

[Neeves]

It seems that many of the respondents got it right first time.

Jonathan

 

[wingcommander]

Thanks Scr0che for the end result to know the definitive and most probably obvious answer.

 

[Poey50]

Turns out the %age reading is a calculation on the BMV and shouldn't be relied on, consumed amp hours is a better measure but is not displayed by default! Mostly likely my reading of the %age has knackered my batteries, ie thinking they are full when they are not. New batteries installed, all working correctly, lesson learnt!

The BMV is a great bit of kit but it relies on the batteries being charged to full in order to re-synchronise the BMV to 100%. If you don't do this you get double-trouble, an unsynchronised battery monitor delivering false information and sulfation setting into the batteries. The false information can then lead you further astray. Getting lead acid back to full as quickly and often as possible is the solution to both issues.

 

[geem]

The BMV is a great bit of kit but it relies on the batteries being charged to full in order to re-synchronise the BMV to 100%. If you don't do this you get double-trouble, an unsynchronised battery monitor delivering false information and sulfation setting into the batteries. The false information can then lead you further astray. Getting lead acid back to full as quickly and often as possible is the solution to both issues.

Agreed. I had a battery monitor on my last boat. I decided not to install one on my current boat. That was 11 years ago. I found that the monitor was more trouble than it was worth. I use battery voltage as an indicator and a few other tricks but if you want a periodic check on battery condition you can't best old fashioned wet cell batteries and a hydrometer. The main source of daily information is my Victron Smart solar app on the phone. With the correct manufacturers charge voltages, absorption time, etc programmed in, you build up an understanding of the charge profile of your batteries. They get to float every day without problem. This is the key to good life on wet and AGM batteries.

 

[Lucy52]

It is quite common for new boat owners to ruin a set of batteries, with the attendant cost and inconvenience. There is a, “battery primer,” on Canal World to address this as it comes up so often, which might be worth the time spent.
Battery Charging primer

edit duplicate text

 

[arcot]

Noticed an interesting pattern with my battery bank which I can't understand.

Victron smart battery monitor, 4x100Ah AGM Exide batteries, less than 12 months old. What I notice is that during overnight passages, when the nav electronics etc are running, once the battery capacity drops to around 80% I see the volts in the monitor at 11.3 (or thereabouts). This doesn't look right, shouldn't it remain at 12.5v until my capacity is being exhausted? The upshot is, my AIS unit is beeping at me with a 12v alarm...

Can anyone explain this behaviour or a possible cause, where to check, what to check? Surely not duff batteries?

Cue dead parrot sketch......

 

[Refueler]

Turns out the %age reading is a calculation on the BMV and shouldn't be relied on, consumed amp hours is a better measure but is not displayed by default! Mostly likely my reading of the %age has knackered my batteries, ie thinking they are full when they are not. New batteries installed, all working correctly, lesson learnt!

A very painful lesson and my sympathy.

A previous poster mentioned a 'Pulsator' - they are sold to revive tired batterys. Another poster says they are 'snake oil'.

I have one and I can say based on actual use :

The Pulsator basically shorts the battery terminals in pulses ..... the idea being to causer the deposits on plates to be dislodged .. and hopefully return to electrolyte ...
Do they work ? Yes and No.

A moderately aged battery can be improved - but not returned to 'as new' .....
A seriously aged battery will not recover sufficiently to be able to provide good service, but may be ok for low wattage duty.
A failed battery is failed - end of story !!

If your batterys still charge up fully - check by isolating and a multimeter as Paul and others have said - using a Pulsator may recover them enough for low draw use ... BUT they take days to work ... which I believe is why so many people find they do nothing ... they don't run them long enough. You would never get them back to original use though ... that is 'snake oil' territory.
The "Pulsator" has basically replaced the old - where many years ago - you could buy a 'potion' to add to the cells that caused the deposits to fall away from the plates ....