Leisure Battery - Heater Drain.

To all you Leisure battery Truma heater experts.
AS Warwick XL ’19
Just arrived back from 20 days in the Hebrides. One particular day we were wild camping (No HUP) and the storm was so bad that it happily prevented us from leaving the camper. So midday out came the papers and gas kettle, & on went the Truma heater set to 18C. No radio/phones or ipads on or plugged in and only 1 led light used for 3 hrs. Unfortunately, about 9pm that night the leisure battery reported 10.2v & the heating stopped. Next day blue skies and the solar panel had the battery fully charged again everything working.
Please...
Does anyone have knowledge of how long the heater will last with no HUP in a cold environment with little or no on board solar panel gain? Is it the physical turning of the heater fan blowing the air that runs the battery down? 
We’re hoping to do the Scotland North Coast 500 next year in cold months. But only one day of warmth from the Truma when wild camping in continual bad weather will take a little extra planning.
So I guess the main question is... 
How long will the Fully charged leisure battery in our Warwick XL ‘19 support the Truma heater for?
All help much appreciated.
KR Devon Dave

Hi Devon Dave
Welcome to the forum from sunny Bridington, lots battery and trauma experts on here.
I would be looking at a second leisure battery myself Dave, especially if your off grid, plenty of sites with EHU on the NC 500"lots of us have done the 500.
Boaby

Devon Dave wrote:that night the leisure battery reported 10.2v & the heating stopped. Next day blue skies and the solar panel had the battery fully charged again everything working.

I'm afraid I don't know the spec of your Truma heater, but something doesn't look right here. Without knowing the size of solar panel or battery capacity it's hard to be sure but it's difficult to see how a 80Ah battery that's completely flat (as a voltage of 10.2V would indicate) could be completely recharged from solar in one late September day, unless your solar panel is pretty big. So I'm wondering if your control panel is giving you misleading readings.

One thing I would say though: if you are planning lots of days in a row off EHU in Autumn/Winter, a second battery alone will not help the situation. At this time of year, you are likely to be constrained by how much power the solar panel can harvest, and not by how much battery storage you have.

Of course, if you change the pattern so that, for example, you are on EHU every other day then the situation could be very different. In those circumstances, doubling the battery capacity could work quite well.

The power consumption of the Truma 6e heater as fitted to the Warwick XL is shown as follows.....


Power consumption (at 12 V): operation of heater and water container
max. 6.5 A for short periods (average approx. 1.4 A)

We have a Warwick Duo (not an XL, but the same heater). With a 90 a/h leisure battery fitted and with quite a bit of heater use, we expect three days use.

As has been said above, you cannot recharge a flat leisure batter in one day (unless your solar panel is really huge) and I would not expect more than about 12 a/h from a sunny, no shadows kind of day at this time of year at the latitude you quote.

I suspect that either, a) your leisure battery was not fully charged to begin with, or b), it is at the end of its useful life and has reduced capacity.

Paul Mold's figures seem about right to me for real world battery use and a 24 hour drain could be as high as 20 a/h (allowing three days use on gas, with modest 12 volt use for lighting etc)