Engine battery not charging off mains

[Strollerbird]

Any help or advice gratefully received.
When we put our motorhome in storage we would occasionally plug it in to charge both the leisure and the motor battery. On the last couple of occasions we have found the leisure battery fully charged but the engine battery dead.
Where do I start to look to solve this?

 

[YeoBlade]

Model of motor home? Is there a switch to change over charging?

 

[trevskoda]

Do as i did, connect a heavy battery cable through a 200amp relay and a dash switch, also handy for a jump start if you forgot to turn lights of.
Or as many do a rhine wire fused at both batteries, just pull the fuse when using the van.
Also is it the van charger which most are junk, best fit a smart charger of around 10amps or more, this with above wire will charge the lot and cycle to desulfer and maintain them.

 

[Phantom]

Maybe a fuse? Ours had a small device that charged the SB at up to 2Ah from LB until if stopped working!

 

[MERL]

I do hope Phil's got this issue covered in his new book because this issue and three way fridges not working on gas has been done to death.

Are you saying that the starter battery used to get maintained when on EHU but now it doesn't?

If so are you taking about the same van?

Can you post a picture of your electrical control panel, that'll help massively.

 

[Strollerbird]

Model of motor home? Is there a switch to change over charging?

Dethleffs Esprit - no switch

 

[Strollerbird]

I do hope Phil's got this issue covered in his new book because this issue and three way fridges not working on gas has been done to death.

Are you saying that the starter battery used to get maintained when on EHU but now it doesn't?

If so are you taking about the same van?

Can you post a picture of your electrical control panel, that'll help massively.

 

[Strollerbird]

Yes starter motor was maintained when EHU was on
Yes - same motorhome

 

[mistericeman]

Link to a manual (incase you haven't one to hand)
So you Can check charging switch positions etc...

https://www.dethleffs.co.uk/dethleffs/00_global/02_pdfs/bedienungsanleitungen/2025/motocaravan/x1513.08.231_motorcaravan_2025_gb_print.pdf

 

[MERL]

According to the manual and what you've reported it would appear that something has gone wrong in the EBL unit and it's no longer supplying a charge to the starter battery. It's possible that there is a blade fuse that's blown but oddly there's no 12V fuse data in those comprehensive instructions. Pull each fuse one at a time and check them preferably with a multimeter, you may get lucky. If the fuses are OK then maybe the simplest fix would be to fit another form.of battery maintainer which wires between the leisure and starter batteries. This would of course keep your starter battery maintained while on hook up but also If you have solar then this secondary maintainer would give you the benefit of keeping the starter battery topped up from the solar that's feeding the leisure battery too, something that the EBL doesn't do.
Cheapest way is a simple fuse between the two battery positives, search Clive Mott battery maintainer.
Ablemail AMT12 can apparently be set to very low voltage drop so the starter battery is kept at a high enough voltage to prevent sulphation, cheaper alternatives (vanbits etc) aren't quite as good in this respect.
The best unit of all in this respect is the DIY design which I posted a while ago on here, it works better than any commercial unit and parts cost about £10-15. You will have to build it yourself though.
Thread 'High performance DIY Battery maintainer.' https://wildcamping.co.uk/threads/high-performance-diy-battery-maintainer.100567/