Flat Engine Battery

Beckie Hawken

Free Member
Oct 27, 2014
I'm a newbie
I've been searching for an answer but have ended up very confused. Our engine battery went flat after 3 weeks idle. What is the best way to keep it charged up please? Do we need a solar panel if so what size? Can anyone give me a link. Or do we need a spare battery - is it ok to keep charging up batteries on a charger? Thanks everyone


Aug 26, 2007
YO11 2BD
Since 2005
Hi Beckie, a solar panel may keep the battery topped up but in winter its unlikely as there are too few sunshine hours per day.
a panel would need to be around 60 to 100 watts to make use of what weak sunshine there is.

If stored at home them a simple modern battery charger will do the job.

Just turn the charger on once a week for 2 or 3 hours.
if the battery still goes flat leave the charger on a bit longer.
if it goes flat after that its had it and needs replacing.


Aug 25, 2014
Hobby 750 tag.
Full timing for five years and loving it!
You can buy a trickle charger that I used on my motorbike. Just leave it on all winter.


Free Member
Nov 13, 2013
3 years and not long enough
Hi, a solar panel or/and a spare battery would be good but it would also be a good idea to check your battery as something must be draining it. Others on here that are more battery aware will be able to list things to check for. Also it all depends on how often you are going to use your motorhome as to whether it is worth the expense of a solar panel


Deceased RIP
Sep 14, 2013
Was a newbie, now a Middie.
Unless the alarm is through the hab battery, John. Mine is. And so easy to re-tune the wireless, better then it going flat and losing the stations anyway.
Mar 16, 2010
TEC Freetec 688ti
25+ years
My battery used to flatten in 2-3 weeks of non use ....discovered it was the radio so now I take the front off after every trip and engine battery is fine.:)


Nov 29, 2013
Classic Hymer B564
Since 1981
We had a constant drain on the engine battery which was, after buying battery No2, eventually traced to having a modern radio fitted to an older Hymer with no auxilary circuit on the ignition switch.

Fitted an off switch to kill power to the radio and problem resolved.

I also fitted an isolator to the ground post of the battery and a battery master due to extended non use periods.

It means having to retune radio on each use but that is simply an auto scan while going through the pre-flight checklist prior to departure.


Beckie Hawken

Free Member
Oct 27, 2014
I'm a newbie
Thank you all for your help. Our battery was new in August when we bought the van so we've been back to the company & they are sending us a new battery. So with your advice hopefully we can keep it charged up


Dec 17, 2013
Herts UK
Burstner Elegance 890
Since 2013
I posted a similar problem on the Motor Caravaners club forum and got lots of advice. I have pasted the most relevant replies (and my original question) below. Regrettably I have taken to having to disconnect my battery when I leave the vehicle otherwise the battery is flat after 3 weeks. That means my expensive alarm is not connected and I have to go through a statey dance to lock the vehicle up each time.

Hope this helps

I would love to know if you do find a battery drain what it is please?

I am new to Motorhomes having just picked up my 2011 Autotrail Arapaho towards the end of July 2013. To my disappointment when I went to my vehicle recently after leaving it for 4 weeks the vehicle battery had insufficient charge in it to start the vehicle. I had left the vehicle with the system shut down, on the advice of the dealer, having previously left the system on, in the expectation that the solar panel would maintain everything charged up. However on that occasion the battery was flat after being left for just 3 weeks.
The advice I have received is to disconnect the neutral terminal to the battery in order to preserve it but this is both awkward and carries with it some issues. 1) I have to activate the centralised locking whilst still inside the vehicle and prior to disconnecting the battery otherwise there is no way that the passenger door can be locked as there is no external key lock or button to press from the inside. I then have to exit via the habitation door. 2) the Alarm (which I paid out to have fitted) cannot be set otherwise as soon as the battery is disconnected the alarm activates.
I would have expected an under 3 year old Battery should last easily more than 4 weeks between visits and I would also expect the solar panel to keep the battery topped up? Or is this naïve? However I am thinking the battery is damaged and needs replacing?
Also can anyone advise the best state to leave the vehicle in if I do replace the battery? System on (to get the charge from solar panel) or off with battery disconnected? And what do I do about the alarm, which for all I know is draining the battery? Regrettably I cannot leave the vehicle connected tot he mains, it is in storage

As Graham suggests giving the 'van a road run for 30 mins or so every 3 or 4 weeks should really be a minimum.
The solar panel may not be wired to charge the engine start battery. This can be altered but beware as no sun / good light means little or no charge and modern vehicles drain small amounts of current all the time the battery is connected.
best regards

Hi & welcome, Unfortunately a 2011 vehicle has a 60 m/amp drain as standard without the additional drain of an alarm system. General rule of thumb is after 3 weeks it will not start. If vehicle is in storage i would recommend a seperate solar panel direct to the engine battery.

It seems that you expect (rightly) that the solar panel should keep the batteries charged. However this will only happen if the panel has been connected in the correct way. Usually panels are installed only to keep the habitation battery charged I suspect that this is the case with your van. What is needed it the addition of a battery master which connects the panel to both the habitation and vehicle batteries and will keep both charged.

I had the same problem as you but after the installation of the battery master have had no problem even after leaving the vehicle in storage for several week. (Advert)

Although I have to agree that the best way of keeping everything in tip top order is to use the van

The problem is that all Auto Trail models from 2011 onwards had the new Sargent smart box/panel/charger fitted and in a move to improve the set up it was decided that the main function of the solar panels is to keep the leisure batteries charged, which is fine when the vehicle is used frequently. What the new set up does not do and where the pre 2011 models did do is switch the charge from the leisure battery/s to the vehicle battery when the leisure battery/s is/are fully charged, hence the problem of a flat vehicle battery. This charge or lack of occurs when the Sargent system is in shut down mode. If the Sargent system is left in standby mode the solar panel will charge both the leisure and vehicle batteries, BUT, there is a downside to that also. To leave the system in standby mode will use some power and at this time of year and over the winter months the system could be using more power than the panles are generating, resulting in........yes, a flat battery. I am told by Sargent that it is possible to fit a switch (2 wires) to the Sargent box to divert the charge from the leisure battery/s to the vehicle battery whilst in storage. The leisure battery/s should not go down if everything is switched off.
How this would affect your warranty I have no idea. It may be worth a call to both Sargent and Auto Trail expressing your concerns about this change to the set up as described as "product improvement"
If any battery is left flat for a period of time it will need replacing and may not be covered by your warranty

First if you have a Radio and an Alarm system fitted which battery are they drawing the power from? if its the Engine battery consider changing them over to the Leisure battery!, particulary if your Solar panel is only connected to the L/B.
If this proves to be the case then also consider fitting a Battery Master which will provide a TRICKLE charge to the starter Battery if its voltage drops 0.5 a volt below that of the Leisure Battery. It might be worth asking the Dealer to provide a new battery, they tend to let them stand on the forecourt for weeks on end without being charged until someone shows an interest. If you do go down the new battery route, a recent test survey , in which 40 different makes of batteries where cut in half to rate their components and construction (Lead plates etc], ONLY TWO makes came up to scratch!!. Banner and Exide.
Regards Hagar

personally would not be happy keeping the N disconnected since a lot of the electronics work on the N side of the system.
The dash charger unit seems to be the best idea. I had to have one when my van was in store on a farm and it kept the alarm happy and worked well. Mind you that was on a Merc. whose Cig. lighter socket was permantly live so I did'nt have to mess about connecting to the battery. Mind you since I assume this is a Fiat chassis there would be a very short run to where the battery is under floor well.
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