Leisure battery expected drain

[Disciple72]

Evening all, hope those that can are taking advantage of the fine camper weather

I've just installed 2 x 120ah AGM Advance leisure batteries in my camper. I also bought a quicklynks BM2 monitor to help keep an eye on their health. When I first installed the batteries they were showing a combined charge of 90%. I put them on smart charge and got them to 100%. Over 2 days the charge has dropped by 4% to 96% even though the van leisure electrics have not been used. Is this normal or should I be investigating a potential issue?

Many thanks for any support anyone can offer.

Cheers

 

[Dellmassive]

That will be fine,

Most likely just the voltage settling..

When you have 7 days worth of data post a screenshot of the bm2 plot.

Of the voltage doesn't show a constant drop over time you are good.

 

[Disciple72]

I'll post an update as you've stated in 7 days.

Cheers

 

[roadtripper]

Are both batteries permanently wired as a bank?

Batteries in a bank will equalise voltage with each other as they will not be identical capacity so when off charge the higher charged one will try and charge the lower charged one until they are at the same voltage.

So long as this is just an initial drop then it's nothing to worry about.

As an aside if you ever have an issue with one battery you'll need to replace both. In a bank the weaker battery will always cannibalise the stronger one so very rapidly your new battery will age to be the same health as your old battery - it seems like a way to save money but it will markedly reduce the battery life of the new battery.

 

[Disciple72]

Hi, thanks for your response. Both batteries are wired up in parallel, so as one big battery of 240ah, both were bought brand-new just over a week ago. I'm losing 3 to 4% daily. I've attached my BM2 plot. When I was in the van with everything switched off the only thing running was PLC screen. The screen was showing a constant draw on the battery of 0.7amps.

 

[roadtripper]

What is the "PLC Screen"?

Do you have a shunt on the battery bank - if so where?

0.7A x 24 hours will be consuming 0.7 x 24 = 16.8 Ah a day which is about 7%

 

[Disciple72]

PLC is the programmable logic controller. Enables timmer on lights, heater, waste water level alarm, Sorry, what is a shunt? Total electrical novice here.

 

[roadtripper]

The "PLC Screen" is displaying battery current for your Leisure bank - how is it doing that?

You have said you have AGM batteries so it cannot be a built in BMS - the only accurate method is a shunt like you have on the starter battery.

A shunt is very high current, low but precise resistance device that when you measure the voltage across it allows you to measure the current at very high accuracy. In vans they are generally installed on the battery negative as it's important all current flows through them.

The point of my questions about what the "PLC Screen" is and the shunt is I'm trying to work out if that current figure is accurately obtained (in which case it will be very useful to track down any parasitic drains) or it's some guestimate made up by the electronics (in which case... not much use)

 

[Disciple72]

I'm going to get my brother to take a look tomorrow, he's an electrical engineer, not auto related, so he keeps informing me lol!!. He's going to test some stuff. I'll show him your comments and come back to you. I appreciate you taking the time to give me your knowledge, so thank you.

 

[roadtripper]

A good thing to get to know your electrics so you can enjoy camping

Make sure you know what's powered from where and where the fuses are.

If the current is measured with enough accuracy then the next stage is to start disconnecting things (usually by pulling the fuse) to find out what's drawing power.

Common culprits are compressor fridges and diesel heaters as they both tend to recommend wiring directly to batteries and are always on, another increasingly common device is USB power sockets as they are active devices and always draw power so should be switched.

 

[Disciple72]

Brilliant, thank you