Are my batteries knackered?

[Ammonite]

12v fridge runs fine off the domestic batteries when the engine is runnimg or the 240v charger is on BUT when just running off the batteries the compressor starts ok but the voltage under load drps away steadily until the fridge low voltage cutout is reached (10.7v according to the manual). Here's a few figures

Engine running:-
Nasa monitor reads 14.4v, receiving charge of 9.2 amps
Voltage across battery terminals while charging 13.92 (multi meter)
Voltage at all swithes in electrical panel 13.97v (multi meter)
Voltage at fridge when fridge off 13.95v (multi meter with 3 m cabl e run to fridge
Voltage at fridge when on and drawing 3 amps 12.8v (multi meter)

Switch off engine:-
Fridge starts drawing 3.5 amps according to Nasa monitor
Voltage at fridge drops to low voltage cut out in a few minutes depending on how long I have run the engine
Voltage at Nasa drops quickly initially and then stabilises at 12.8v dropping fairly slowly so its at at about 12.6v when the fridge stops
Both domestic batteries have a green battery ok indicator


Any guidance much appreciated!

 

[yachtorion]

Sounds like they might be yes, assuming the batteries are well charged?

What happens to the voltage on the Nasa if you turn the fridge and chargers off but run some other fairly high current drain like turning on all the lighting (assuming non-LED)?

What kind of batteries, what capacity, how old?

 

[maby]

They certainly don't sound healthy from your figures..

 

[Phototropic]

The voltage on the NASA sounds like battery is fine 12.6-12.8v shortly after alternator voltage drops off is what happens on mine.

But if voltage is dropping on multimeter at the fridge sounds like battery could be gone - or the NASA is wrong?

If battery stays around 12.6v at rest it sounds like its healthy...could test each one under discharge voltage with multimeter to eliminate risk NASA reading is wrong? You only provide voltages under charge which represent the volatage of the Alternator basically.

Is the NASA wired to one domestic battery and the fridge the other?
Have you got an isolator to try one battery or the other and see if one is running ok?

As suggested to check its not the fridge maube try some other high current drain and see if voltage starts dropping there too?

 

[Ammonite]

Sounds like they might be yes, assuming the batteries are well charged?

What happens to the voltage on the Nasa if you turn the fridge and chargers off but run some other fairly high current drain like turning on all the lighting (assuming non-LED)?

What kind of batteries, what capacity, how old?

They are Lucas 110ah leisure batteries about 4 years old. When I switch on the water pump which draws even more amps the voltage drops even further at the pump but of course that doesn't cut out. But I can leave the boat for a couple of weeks and the voltage on the nasa will only drop say 0.1v with everything bar the Nasa switched off

 

[maby]

They are Lucas 110ah leisure batteries about 4 years old. When I switch on the water pump which draws even more amps the voltage drops even further at the pump but of course that doesn't cut out. But I can leave the boat for a couple of weeks and the voltage on the nasa will only drop say 0.1v with everything bar the Nasa switched off

Does the voltage recover following a period of no load (without charging, obviously)? If so, I believe that indicates sulphation - might respond to a regenerating charger.

 

[Ammonite]

Its Nasa bm1 battery monitor btw

 

[Phototropic]

Is there a difference after a period of heavy discharge on pump/fridge between voltage at the BM1 and voltage across each battery at the multimeter...

(i find these things are usually a process of elimination)

 

[TQA]

Sounds like you have voltage drop on the line to the fridge.

Clean all connections on the line and try again. Anything above 12.2 volts at the battery under a 4 amp load should still drive the fridge.

 

[yachtorion]

They are Lucas 110ah leisure batteries about 4 years old. When I switch on the water pump which draws even more amps the voltage drops even further at the pump but of course that doesn't cut out. But I can leave the boat for a couple of weeks and the voltage on the nasa will only drop say 0.1v with everything bar the Nasa switched off

Then yes sounds like your batteries have lost most of their capacity. As mentioned by maby could be worth trying a high quality charger (e.g. c-tek) with anti-sulphation tech.... otherwise it might be new battery time.

 

[Ammonite]

The battery charger is a Waeco IU252a which I believe is a pretty sophisticated charger

 

[yachtorion]

A quick look at the brochure suggests that while it is a sophisticated charger it may not have the anti-sulphation option, though I have no idea how well that works anyway.

Hopefully someone else will have some better news/ideas for you, but otherwise might be new battery time.

 

[SHUG]

Battery voltage is onlt part of the story.
As other posters have pointed out, you can lose both capacity and current capability without the voltage dropping. As they are sealed units the level of the battery acid could have dropped (hmmmm...I note that green indicators are showing). The best bet is to borrow a battery tester from your friendly local garage and see what the voltage drops to when 50 amps or so is taken from the battery or see what the battery voltage drops to when the starter motor is operated.
OR the fridge low voltage sensor could be dead. Have you checked the voltage across it when it cuts out?

 

[maby]

A quick look at the brochure suggests that while it is a sophisticated charger it may not have the anti-sulphation option, though I have no idea how well that works anyway.

Hopefully someone else will have some better news/ideas for you, but otherwise might be new battery time.

It's not a silver bullet, but I have seen a sulphation buster make a useful difference to a tired battery - possibly worth trying to borrow one and give it a whirl.

 

[GHA]

OR the fridge low voltage sensor could be dead. Have you checked the voltage across it when it cuts out?

Sounds like a much better place to start looking if the nasa is reading 12.6v when the fridge cuts out. Suggests the batteries are not the culprit here. Like TQA said. I had some very strange behavior from a danfoss when the thermostat was slowly dying.

 

[pappaecho]

I had a similar problem over the winter on two 110 amp "Leisure" batteries. The bank would not hold its charge. Separated each battery and monitored the discharge rate. One was very bad. the other OK. Replaced the bad battery and now OK.
I think that the bad battery was drawing current from the good one, and that the bad one had a cell gone
Good luck

 

[Ammonite]

Sounds like a much better place to start looking if the nasa is reading 12.6v when the fridge cuts out. Suggests the batteries are not the culprit here. Like TQA said. I had some very strange behavior from a danfoss when the thermostat was slowly dying.

Voltage at the fridge when it cuts out is 10.9v while Nasa is reading 12.6v. This is when the engine is off. I'm using a cheapo multi meter but it's close enough to the 10.7v cut out to make me think the fridge is fine. The voltage at the fridge under load when the engine is running or the charger is on stays over 12 volts

 

[Ammonite]

I had a similar problem over the winter on two 110 amp "Leisure" batteries. The bank would not hold its charge. Separated each battery and monitored the discharge rate. One was very bad. the other OK. Replaced the bad battery and now OK.
I think that the bad battery was drawing current from the good one, and that the bad one had a cell gone
Good luck

Thanks - will try this

 

[William_H]

As said OP needs to check and improve the total cabling to the fridge to reduce voltage drop to less than .2 volt. A multimeter can be used checking actual voltage drop pos of battery terminal to pos at fridge and likewise neg of battery terminal to neg at fridge for actual volt drop. Can be use din asimilar way to check parts of the circuit ie switches etc.
Having got the volt drop improved then if OP still doubts the batteries separate the 2 batteries and compare performance of each under load. It is quite liekley one will be worse than the other. good luck olewill

 

[Spi D]

All good advice. Battery life is heavily affected by the number of deep discharge cycles, which is where battery types (starting/domestic etc.) differ.
Starting batteries like to stay near full capacity at all times and actually will when used for short delivery of high power to start a (willing) engine.

Definitely agree with separating the batteries to check them individually. Bear in mind that 'intelligent' multi stage chargers need to complete all stages (takes some time..)

After a full charge, check voltage, leave the batteries alone and re-check regularly for an hour or two. Readings should stay at or above 12.6 v if batteries are good. 12.4 v indicates 'replace soon', 12.8 v or more is "Very good".

Built-in status 'eye' showing green (or anything) may be wrong.

After the above test to know battery state I use this inexpensive (~£ 22) tool for load testing