Battery drains from 100% to 50% in 14 days?

WelshGas said:

Which battery showed 12.3V? Front or Rear?

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It was the rear one.

Are you sure those are new (since last may , said in the first post) batteries ?
Imo looking at the picture , those could be older ones and therefore few years old ...

hotel california said:

Are you sure those are new (since last may , said in the first post) batteries ?
Imo looking at the picture , those could be the original ones and therefore almost 10y old ...

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Originals are usually Varta, as far as I know. based on googling around. These are not 10 years old.. might just be my photography I do believe the motorhome centre changed them, just not sure they put the right ones in.

Looks like the battery spec is not AGM, would this cause an issue with charging from the alternator / EHU? I seem to remember reading somewhere that the VM charging system is configured for AGM battery types?

Here´s a pic of my original rear one.

These batteries are used as Leisure Batteries, so I think they are acceptable But, I would have expected them to have very similar voltages if they were being properly charged from either the built in Mains Charger or the Engine Alternator Split Charge System.

When the Mains Charger is On, do you get the Plug symbol on the Control Panel?
Likewise I presume you get the Generator symbol when the engine is running?

If that is the case then I think one of the Batteries, the rear one, may be faulty.

WelshGas said:

These batteries are used as Leisure Batteries, so I think they are acceptable But, I would have expected them to have very similar voltages if they were being properly charged from either the built in Mains Charger or the Engine Alternator Split Charge System.

When the Mains Charger is On, do you get the Plug symbol on the Control Panel?
Likewise I presume you get the Generator symbol when the engine is running?

If that is the case then I think one of the Batteries, the rear one, may be faulty.

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Yes to both. I think you are right, I’ll see if the conditioning charger has any +ve effect on the rear one. thanks!

The original battery is a Varta Professional Dual Purpose AGM, 80 Ah, 800A, Short code: LA80.
Same battery different label: Varta Silver Dynamic AGM, 80 Ah, 800A, Short Code: F21.
Those batteries have the following measurements: 315x175 mm, height 190 mm.

For the rear battery to have a lower voltage there can only be two causes:

1) The cube fuse is blown. Most likely. Look at the square fuse under the rear battery live terminal (under the big red plastic cap). Check if the metal rings on its top and underside are linked via a thin metal strip under teh perspex inspection window on the side of the fuse. You need to remove the fuse to check really.

2) The rear battery is faulty. Far less likely.

Even leaving them just conected together with no charging at all for a while should equalise their voltage . They should come out of the van with near identical voltages.

Your cube fuse is most likely blown and you've just been running off the front battery. Hence it came out nicely charged - 13.1v - hot off the charger, whereas the rear is effectively disconnected and sitting dormant at 12.3v. Not being used, nor charged.

btw 12.9v isn't "100%" (as per your graph). It might be 12.9v when the VW panel says 100% but a lead acid battery at rest (not being used, nor charged) is 100% at 12.6v. 12.3v isn't 50% used.

BTW - as to why the cube fuses are blowing is a mystery to me. Until 2 days ago I'd assumed that over time, one battery had been replaced when the other one was flat or vice versa, and the charging current needed to equalise the batteries blew the fuse.

However....

I fitted one of my solar kits to van less then 6 months old on Friday. I was extremely careful when removing the battery (rear) - which has an insulated protective cap. I inspected the fuse (I alwasy do now) and it was blown!

How on earth a nearly new van with two batteries in great condition has a blown fuse is a mystery to me. The owner could not fathom it either.

I would estimate that 1/4 of the vans I see have blown cube fuses. I carry a stock now as one of my customers was charged £80 by VW to supply and fit a one!! (and this was when I'd removed the battery for them!)

Andrew Dyer said:

Looks like a good gadget.. you have found my weakness. I might 'need' one of those

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I got one of these after reading about it through a previous post by @WelshGas A great bit of kit and I’ve used it to reset my airbag light a number of times due to us spinning passenger seat and pulling on loom underneath. Had it checked by VW a few times but they wanted £80 a shot to do the same thing - didn’t seem interested in fixing the problem. Ive used it on my Audi and our VW Polo as well. Very handy.

Roger Donoghue said:

For the rear battery to have a lower voltage there can only be two causes:

1) The cube fuse is blown. Most likely. Look at the square fuse under the rear battery live terminal (under the big red plastic cap). Check if the metal rings on its top and underside are linked via a thin metal strip under teh perspex inspection window on the side of the fuse. You need to remove the fuse to check really.

2) The rear battery is faulty. Far less likely.

Even leaving them just conected together with no charging at all for a while should equalise their voltage . They should come out of the van with near identical voltages.

Your cube fuse is most likely blown and you've just been running off the front battery. Hence it came out nicely charged - 13.1v - hot off the charger, whereas the rear is effectively disconnected and sitting dormant at 12.3v. Not being used, nor charged.

btw 12.9v isn't "100%" (as per your graph). It might be 12.9v when the VW panel says 100% but a lead acid battery at rest (not being used, nor charged) is 100% at 12.6v. 12.3v isn't 50% used.

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Thanks. I've attached a picture of the cube fuse, on the basis I can't see well through the inspection perspex and there are signs of corrosion around the ring of the connector. I think a clean up of the connector and a replacement fuse would be a good move!

Roger Donoghue said:

I would estimate that 1/4 of the vans I see have blown cube fuses. I carry a stock now as one of my customers was charged £80 by VW to supply and fit a one!! (and this was when I'd removed the battery for them!)

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Where do you get your stock from? I'm hoping VW run some thorough diagnostics on the wiring if they are charging that! Is aftermarket ok, I would hope a 'fuse is a fuse'?

I like the look of your solar panels BTW, but I need to get the basics squared away first

hotel california said:

Read some older threads on thseame issue ....so much things to look at .
Start with checking the two les.bats are connected correct and fuses are ok so both are working and not just one .

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@Andrew Dyer , did you not check the fuses last week on advise of the above post?

If a decent VW dealer had changed the batteries they probally had changed the fuse also if it looked like it does on the pic above...

Not worth the trouble changing/charging the batteries if is the fuse is dead .

I was told if the cube fuse is blown something major is or went wrong with the electrics and better to have it fully checked .
Thats one of the reasons carrying a spare of those is not needed as you should bring the Cali in anyway and the fact it's a delicate thing to do while on the move(taking out the battery ) ...it's not just plug&play as with small fuses

Also not at all convinced by someone above saying 1/4 Cali's the cube fuse is broken.
That would mean a lot more would be on here asking about the fuse , mine is in 6y and never had an issue but i try to stay away from DIY on the electrics of my Cali.

hotel california said:

@Andrew Dyer , did you not check the fuses last week on advise of the above post?

If a decent VW dealer had changed the batteries they probally had changed the fuse also if it looked like it does on the pic above...

Not worth the trouble changing/charging the batteries if is the fuse is dead .

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The motorhome company was not VW. Batteries are fine, it is definitely the fuse. Just took it out and the two bits of fuse that should be connected separated in my hand. I missed the fuse, but by the looks of it so did the technician that changed the battery in the first place.

Andrew Dyer said:

Where do you get your stock from? I'm hoping VW run some thorough diagnostics on the wiring if they are charging that! Is aftermarket ok, I would hope a 'fuse is a fuse'?

I like the look of your solar panels BTW, but I need to get the basics squared away first

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Cube Fuses
https://www.12voltplanet.co.uk/battery-terminal-cube-fuses-50-300a.html

hotel california said:

@Andrew Dyer , did you not check the fuses last week on advise of the above post?

If a decent VW dealer had changed the batteries they probally had changed the fuse also if it looked like it does on the pic above...

Not worth the trouble changing/charging the batteries if is the fuse is dead .

I was told if the cube fuse is blown something major is or went wrong with the electrics and better to have it fully checked .
Thats one of the reasons carrying a spare of those is not needed as you should bring the Cali in anyway and the fact it's a delicate thing to do while on the move(taking out the battery ) ...it's not just plug&play as with small fuses

Also not at all convinced by someone above saying 1/4 Cali's the cube fuse is broken.
That would mean a lot more would be on here asking about the fuse , mine is in 6y and never had an issue but i try to stay away from DIY on the electrics of my Cali.

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Because of the way these fuses are made, very easily damaged when fitting and prone to damage from vibration. Carrying a spare and replacing a blown/damaged fuse is a perfectly reasonable step to take. However, if it blows when reconnecting or shortly afterwards then does need checking out. The fuse is inline with the connection to the front battery only, so if it blows then this means the front battery is drawing a large current from the rear or the red cable connecting the 2 batteries has shorted to the body which is very unlikely and anyway the Front Battery does not have such a fuse fitted only the rear, so the front battery would be in trouble also.

hotel california said:

@Andrew Dyer ,

Also not at all convinced by someone above saying 1/4 Cali's the cube fuse is broken.
That would mean a lot more would be on here asking about the fuse , mine is in 6y and never had an issue but i try to stay away from DIY on the electrics of my Cali.

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When you say you are not convinced (by "someone" - that's me) are you basically saying I'm making it up?

I'm a little bemused by the comment. I'm telling the truth I can assure you.

I've fitted solar kits to a LOT of Cali's over the last two years and I can assure you, the cube fuse is frequently blown. Frequent enough I stock them and always continuity test the existing fuse, then my replacement once installed to make sure it is still good.

The reason lots of people are not on here posting about blown fuses is that no one I've yet met was aware their fuse was blown......

Also, when you state "i try to stay away from DIY on the electrics of my Cali.[" I would be grateful if you consider that I'm a paying forum sponsor and don't appreciate the idea of DIY kits being talked down by you, particularly as you are a forum moderator.

@Roger Donoghue , saying 1/4 Cali's riding arround with a cube fuse beeing broken is just not realistic imo.
You probally get to see much of those fuse broken as you are in that bussines but most of the Cali owners never have to deal with a broken cube fuse on the rear lesure bat. it's your personal experience maybe but not the general number (25%...?)

The fact i say that i try to stay away from DIY on the electrics is a personal view , i have done some small works like changing the bendy light to a 12v socket and changing a simple fuse or lightbulb but things like changing the lesure bats, working on the fridge , controlpanel ,engine electrics ....i from my view feel that this be done by people with California knowledge .
My words where " i try to stay away from DIY ...." and not "everyone should stay away from DIY ...." slightly diffrent view .

It has nothing to do with any forumsponsor selling DIY kits whatsoever .
I've done some DIY on mine but one should know theire own skills and stay with those...

Guess the OP had bad luck someone changed the batteries not knowing to check the fuse and now probally is using only one lesurebat.