Batteries Discharging

[dolabriform]

Hi all

I have 4 110AH batteries, lead acid, connected in series. They are approximately 4 years old.

During a recent trip, I got a low-voltage alarm saying the batteries were at 10.6V. I put on the engine to recharge them and all was fine. Looking back on it now, I'm wondering if the shore power was not connected properly for the 2 days we were in France, We got the alram 7 hours after leaving.

Since then, I've had the batteries on shore power. I disconnected them all from each other and the boat, and left them for 24 hours, after which they were each showing 13V.

I connected everything back up yesterday, and left the fridge and auto bilge pump on, plus the battery monitors. The charger is not connected.

Since then, I've been seen some big voltage drops followed by recovery. I've atatached the voltage plot from the Victron VRM remote monitor. Unfortunately I don't have the Victron battery monitor in place so I can't see current.

Whilst I was onboard yesterday, the battery monitor I have was showing normal current draw for the fridge, and the bilges are dry.

My mad thought is that this shows that one battery is knackered and dropping voltage, and then the others in the bank recharge it.

I know the only thing to do is load test each battery individually, and in reality, I should replace the whole lot given that the voltage dropped so low, but I'm curious what could cause the pattern on the voltage plot?

Thoughts?

 

[jakew009]

Looks more like you have a loose connection somewhere that is intermittent.

Perhaps try turning the bilge pumps on and see what happens to the voltage.

 

[lustyd]

It could well just be something cycling on. The load will cause the voltage to drop.
Good opportunity to switch to lithium, a single 300Ah battery will have more usable power than you have now.

 

[dolabriform]

It could well just be something cycling on. The load will cause the voltage to drop.
Good opportunity to switch to lithium, a single 300Ah battery will have more usable power than you have now.

I can't fit a 300AH Lithium battery in the space; it has to be a low-profile ( 190mm high ) battery.

As for somthing cycling on, that would be my first thought, but that's a big load to drop the voltage so much given that it's only the fridge and bilge pump plugged in.
Also, the timing looks odd.

 

[jakew009]

I can't fit a 300AH Lithium battery in the space; it has to be a low-profile ( 190mm high ) battery.

As for somthing cycling on, that would be my first thought, but that's a big load to drop the voltage so much given that it's only the fridge and bilge pump plugged in.
Also, the timing looks odd.

If the batteries are knackered even a small load could cause it.

 

[GEM43]

Last summer I had something similar with 6 x Victron Super Cycle AGMs 115ah, three years old. Had the batteries tested, one was said to be “end of life”. I swapped it out for new and not had a problem since.

 

[[70521]]

What was your power draw when you had the alarm?

 

[dolabriform]

Last summer I had something similar with 6 x Victron Super Cycle AGMs 115ah, three years old. Had the batteries tested, one was said to be “end of life”. I swapped it out for new and not had a problem since.

Thanks, I was hoping it was something like that.

 

[dolabriform]

What was your power draw when you had the alarm?

Not a huge amount. The instruments and plotter were on, as were the fridge, auto-pilot, and VHF. The peak load was probably 5 to 8 amps.

 

[Boater Sam]

I bet that they are in parallel, Not series!
How they can all individually be at 13v when not connected together or to the boat is beyond me. Check again with them all disconnected fro each other and the boat. To sit individually at 13v for any length of time when off charge is not possible.

 

[dolabriform]

I bet that they are in parallel, Not series!
How they can all individually be at 13v when not connected together or to the boat is beyond me. Check again with them all disconnected fro each other and the boat. To sit individually at 13v for any length of time when off charge is not possible.

Your right, they are parallel, brain not working.

You say it’s not possible, but after isolating them all and leaving them overnight, that’s what my multimeter was showing when I tested them.

 

[Boater Sam]

Put a new battery in the meter or check against another, a LA battery will not stay at 13v overnight disconnected.

 

[KompetentKrew]

Getting the current meter sorted is worth the investment here. Less than £100 for a SmartShunt, I think?

 

[simonfraser]

If the batteries are knackered even a small load could cause it

I can't fit a 300AH Lithium battery in the space; it has to be a low-profile ( 190mm high ) battery.

As for somthing cycling on, that would be my first thought, but that's a big load to drop the voltage so much given that it's only the fridge and bilge pump plugged in.
Also, the timing looks odd.

this one is 190mm wide, lie it on its side ?

Other suppliers too no doubt

Lithium Leisure Battery - Fogstar Drift 12v 300Ah

 

[PaulRainbow]

I can't fit a 300AH Lithium battery in the space; it has to be a low-profile ( 190mm high ) battery.

Dave, you could buy 4 x 280ah Eve cells and fit them on their side, only 172.5mm then.

EVE LiFePO4 280Ah Prismatic Cell (Grade A)

 

[dolabriform]

Getting the current meter sorted is worth the investment here. Less than £100 for a SmartShunt, I think?

I have a Victron Battery monitor ready to fit, just need to run the cables.

The plot above is from the Victron VRM I have on board. Even if the meter I used was not measuring properly, the Victron plot starts at 13V and then drops.

I'm not really fussed if the meter was a bit out, I'm more interested in what the pattern of those drops is. It's happening every 4 or 5 hours, and I can't think of anything that is switched on that would cause that pattern.

Anyhow, I'm going to order 4 AGM batteries tomorrow. I haven't found a lithium that will fit in the space I have which is built for 4 x 110AH Batteries.

 

[dolabriform]

Dave, you could buy 4 x 280ah Eve cells and fit them on their side, only 172.5mm then.

EVE LiFePO4 280Ah Prismatic Cell (Grade A)

\Hi Paul, that's interesting. I presume I'd need a BMS and other gubbins to go with it?

 

[PaulRainbow]

\Hi Paul, that's interesting. I presume I'd need a BMS and other gubbins to go with it?

BMS, fuse, DC-DC charger. Feel free to get in touch if you want any assistance. Currently sitting in the marina at Ramsgate.

 

[dolabriform]

BMS, fuse, DC-DC charger. Feel free to get in touch if you want any assistance. Currently sitting in the marina at Ramsgate.

Thanks Paul

 

[KompetentKrew]

I have a Victron Battery monitor ready to fit, just need to run the cables.

The plot above is from the Victron VRM I have on board. Even if the meter I used was not measuring properly, the Victron plot starts at 13V and then drops.

A current meter doesn't measure in volts - it tells you the amps being drawn.

You can see this in the screenshot you posted - the amps reading is a flat orange line at 0A, because you haven't got it set up properly yet. Is it a shunt you have to fit?

I'm more interested in what the pattern of those drops is. It's happening every 4 or 5 hours, and I can't think of anything that is switched on that would cause that pattern.

Wouldn't it be helpful to see if there was a large current being drawn when these voltage drops occur?

If so, that's your problem basically solved right there - it's nothing to worry about, you just have to figure out what's drawing the power. If not then I would guess at a bad connection of some kind, and those can be hell to track down.