Motorhome Batteries


The Following article is written by Dave Newell of Dave Newell Leisure Vehicle Services.  A motorhome enthusiast and long time sponsor of MotorhomeFun; Dave provides a high quality service to leisure vehicle owners, whether the vehicle is a car, caravan or motorhome.   Dave fits all sorts electrical equipment is also able to source most components for leisure vehicles. 

Morning Campers

Lots of people ask me about leisure batteries and charging them and there is an awful lot of misinformation about regarding this so I’ll try and clarify a few points for you.  Think of the battery as a fuel tank and it becomes obvious that you have to “fill” it before you can use it.  There are several ways of charging a leisure battery, it should take charge from the alternator when the engine is running, it can be charged via a mains powered charger, it can be charged via a solar panel or from a 12 volt generator such as the two stroke Gasperini unit or a fuel cell.  How long it will take to charge will depend on three main factors, the capacity of the battery, the present state of charge of the battery (how full or empty it is) and the available charging rate (how many amps the charging system can supply).

The Gasperini Self-Energy EG20

Charging from the engine driven alternator on the face of it should be the fastest method because the alternator is often capable of 90 amps or more, if the battery capacity is 90 Amp Hours and it is completely flat then the alternator could recharge it in  about one hour yes?  Unfortunately not as the alternator output may well start out at a high level but it will very quickly drop off to a low level, effectively a trickle charge.  One way to improve this situation is to fit a Battery to Battery (B2B) charger such as the Sterling or CTEK offerings, these devices fool the alternator into producing higher current for longer periods to recharge the battery faster.  The most popular Sterling unit can pass 45 amps while the CTEK unit does 25 amps.

The on board mains charger fitted in most European motorhomes is generally rated at around 20 Amps so that would take 4.5 hours to recharge our battery, many on board chargers are so called “intelligent” units in that they constantly monitor the battery condition during charging and once it is full they will cut off and go into a maintenance mode, older more basic chargers were quite capable of overcharging a battery because they were a simple unregulated voltage transformer often capable of up to 17 volts output.

The Sterling Battery to Battery Charger

Solar charging can be very effective but it does need sunlight (obvious I know). Solar panels have a large surface area for a relatively low output, a 130 watt panel has a surface are of nearly two thirds of a square metre and at best can be expected to give about 7-8 amps, at this level it would take about 11 hours to fully recharge our battery although in reality it will take longer (probably at least twice as long) because the panels output will vary considerably as the sun travels across the sky.

12 volt generators are a good solution although they do burn expensive fuel and produce noise and fumes.  The Gasperini EG20 unit has a two stroke motor driving a dynamo which can give up to 20 amps so in theory at least this would take 4.5 hours to recharge our battery.  Efoy fuel cells are an alternative type of 12 volt generator, they produce much lower current but are near silent and can therefore run overnight to recharge the battery.  The downside of fuel cells is their cost.

At the recent New Years meet at Wrenbury I gave my leisure batteries a serious workout.  In our Iveco Turbo Daily camper we have 3x 110AH leisure batteries (330AH total capacity), there is a 155 watt solar panel on the roof and a CTEK 25 amp B2B unit.  Before we left home I had the van on mains charge (CTEK 7 amp charger) for 24 hours to make sure we had the maximum life in the batteries.  I was a little surprised to find that by teatime on Thursday (2nd day) the batteries were down to 12.2 volts ( fractionally over 50% state of charge)and as its not a good idea to repeatedly discharge batteries below 50% I dug out my little generator and hooked up my workshop CTEK 25 amp charger. Four hours later we were back to around 80% state of charge.  Two days later I again needed to run the generator to recharge the leisure battery bank.

This makes our batteries look as if they are not in the best of health but in fact they are fine, you need  to look at how much power you use before you condemn the batteries.  We have a 100 litre compressor fridge, we watched TV for an average of three hours a day and listened to the radio for an average six hours a day.  Our Propex heating was running for an estimated 10 hours a day plus there’s the lights and water pump to consider.  I measured the current consumption of each item individually then multiplied the current by the hours used in a day to arrive at a reasonable estimate of power used, the fridge runs for about 15 minutes per hour hence the six hour figure against it.

As you can see the bigger users are the fridge and the heater but even the two relays controlling the fridge and lights add up to 9.6 AH per day.  You can see that after two days we had used close to 50% of our capacity.  As for the solar panel well all I can say is its performance was dismal but so was the weather and with the sun so low in the sky its hardly surprising, the highest current I saw from the panel was just 1.4 amps at about 11 am on the brightest day we had.  I would estimate the panel managed to produce approximately 2 AH per day on average.  One area I intend to improve on is the control relays, I’m presently using ordinary automotive 30 amp relays which take 0.2 amps each to keep on. The circuits they control don’t carry anything like that current so I can switch to smaller relays that will draw a lot less current themselves.


About Author

Jim is a long time motorhome enthusiast travelling extensively in the UK and Europe. Averaging 12000 motorhome miles a year. He has owned many motorhomes both British and Continental. His present motorhome is a 27ft C class RV.


  1. Dave thank you for taking the time and trouble to write for FUN I look forward to reading many more of your helpful articles

  2. Hi Dave, Very interesting. However I am a bit technically challenged. Where does the B2B charger fit in the scheme of things? I have an Aldi ‘intelligent’ charger which is still sitting in its box after the last offer. From other threads, I think it may be like the CTEK (I stand to be corrected). How should I use it?

  3. We have used a Gasparini Generator for the past 4 years. We found it very good and quiet. After about 500 hours of use we had a service which involves replacing the exhaust and sparking plug. This is also a labour intensive operation as the unit has to be removed from the vehicle and replaced afterwards.

    After this service all seened well until we heard a jingling noise and found that the internal coolng fan had disintergrated. This was replaced but after a further short period of use 30 hours it disintergrated again. This was replaced under guarantee.

    After 800 hours of use it again failed. This time it needed new bearings and although the dealer replaced the outer ones the main bearing is a factory only repair.

    The unit has a life expectancy of 1500 to 1800 hours befor a new engine and generator unit are required ours need this done after only 800 hours as we have been using it quite a lot fulltiming for the past two years. The factory condemed our internals and we now have a new engine and generator in our old case. We think the fan going, had unbalanced the engine and this lead to premiture wear.

    Factory recommended a service every 300 hours, A wew fan at 500 to 800 hours and new generator at 1500 to 1800 hours.

    Gasparini are currently in administration but we understand that there may be potential buyers in the offing. Meanwhile we had good service from Snr Gasparini when we took our unit to Bologna to have the work done in the factory early in Feb 2012 despite the snow.

    In comparison EFOY cells have a life expectancy of only 1000 hours at a similar cost

  4. Arthur Roberts on

    When it comes to batteries in the motorhome I must be very lucky. I have two 85 Ah batteries – the old fashioned lead/acid which need topping up with distilled water. One came with the vehicle when new in 2003 and the other from my caravan, bought in 2001. They are charged by the vehicle, mains plug-in or solar panel. They regularly show a charge of 13.4 increasing to 14.6 now and again. They run the lights, radio, TV, Satellite box, slow cooker, hair drier, computer charger and other occasional plug-ins via the 800 amp inverter. The lights are LED bought from China (internet) about £1 each and use much less juice. a recent check of the batteries by my local specialist showed they are still in tip-top condition with no sign of failure. Who’s a lucky boy then.

  5. robert lennon on

    hi i need to replace my motor home leisure battery it sais 85amp on battery can i change to a higher rating with out causing any problems to van or charger

  6. trevor willis on

    Interesting.Very interesting.but you are not a jedi yet.use the force.I wont tell you again,The emperor is not so forgiving

  7. Whilst travelling we noticed that the leisure battery was overheating and starting to emit a smell. On stopping the battery was hot and hissing as in overheated. Checking the charge inside the motorhome it was off the metre. A new battery was purchased and connected however the charge registered was still showing off the metre after travelling a short distance. The battery was disconnected and at present we have no leisure battery for fear of damage and more expense. If hook up required we are currently operating without the leisure battery.
    Are you able to point us in the right direction as to the problem.

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