Battery size

[Richard_374377620]

My 12volt leisure battry needs replacing on the 2nd hand caravan I bought (not lasting more than a few minutes with light load). I am likely to occaisionally use sites without mains power for long weekends of 3 nights so need one that will cover me for this with sensible use but I do have a TV (40watt) that we use for about 2 hours during dark nights. I can squeeze a 105 or 113 Ah battery into the compartment and the price is not an issue BUT their extra weight compared to a 85 Ah battery may be (caravan is naturally nose heavy and battery compartment is forward of wheels). Would a 85 Ah battery be suitable for long weekends without mains power or should I go for 105/113 and either remove the battery for travel (pain) or load awning slightly aft of wheels but still staying close to the wheels for stability?

From what I have read and calculated myself I think a 85 Ah battery should cope, just. Your experiences/thoughts would be appreciated.

 

[Richard_374377620]

Futher to the above, my other thought is that I buy an Alko underslung spare wheel carrier (if one will fit my 1995 Swift Azzura 340) and move my spare wheel from the gas locker to just aft of the wheels which would give me plenty of weight loss from the front to allow a heavier battery with 105/113 Ah.

 

[ProfJohnL]

Hello Richard,

Even with 2 hours of TV my guess is that your total daily battery usage will amount to no more than 20Ah, so a fully charged 85Ah battery is likely to last about 4 days - less in winter because of the extra lighting and blown air fan heating you may need.

But despite that margin if you can fit a larger battery then that will give you extra assurance. As for the weight distribution, yes the bigger battery will weigh more, and even with the battery box being in front of the axle, not all the extra weight will be translated to the nose weight, because of the leverage. In practice you should find it not to difficult to rebalance, and certainly moving the spare wheel is likely to more than compensate.

Alternatively moving the awning rearwards may be cheaper and just as effective.

If the extra weight of a bigger battery does affect the towing stability, then it suggests that you must have a poorly loaded or matched outfit now, and you should look into redressing that before adding anything extra. But for most people, I doubt that the extra weight of of a bigger battery will significantly affect the overall towing experience.

 

[Dave_374330759]

Don't forget that unless you've used a smart charger to fully charge the battery it will only get charged up to about 80% of it's rated capacity anyway so your 85a/h battery will only have about 75a/h of usable capacity and as you should never discharge a battery below 50% to avoid premature failure,you've only got about 35-40a/h to play with. The battery a/h rating is usually given at the c/20 rate and will be reduced if you discharge at a greater rate. C/20 for an 85 a/h battery is 4.25a = 51watts, whereas a 110a/h will be happy at 5.5a = 68watts. So if you want to maximise your battery life (both in usage and in years) go for the biggest one you can get in the box

 

[Richard_374377620]

Hello Richard,

Even with 2 hours of TV my guess is that your total daily battery usage will amount to no more than 20Ah, so a fully charged 85Ah battery is likely to last about 4 days - less in winter because of the extra lighting and blown air fan heating you may need.

But despite that margin if you can fit a larger battery then that will give you extra assurance. As for the weight distribution, yes the bigger battery will weigh more, and even with the battery box being in front of the axle, not all the extra weight will be translated to the nose weight, because of the leverage. In practice you should find it not to difficult to rebalance, and certainly moving the spare wheel is likely to more than compensate.

Alternatively moving the awning rearwards may be cheaper and just as effective.

If the extra weight of a bigger battery does affect the towing stability, then it suggests that you must have a poorly loaded or matched outfit now, and you should look into redressing that before adding anything extra. But for most people, I doubt that the extra weight of of a bigger battery will significantly affect the overall towing experience.

Hi John, thanks for the info.

20 Ah is what I thought I would use, good point about the fan in the winter time though as I will be using it in the winter.

The caravan tows fine but is close to nose weight limit of my car even before I load in the gas cylinders never mind anything else in the gas locker.

From what you have said, think I will go foe large battery as possible and either throw the spare wheel in the car for now until I get an Alko carrier as I will eithet be leaving awning behind or getting a light weight porch awning.

Thanks again for your help.

 

[Richard_374377620]

Don't forget that unless you've used a smart charger to fully charge the battery it will only get charged up to about 80% of it's rated capacity anyway so your 85a/h battery will only have about 75a/h of usable capacity and as you should never discharge a battery below 50% to avoid premature failure,you've only got about 35-40a/h to play with. The battery a/h rating is usually given at the c/20 rate and will be reduced if you discharge at a greater rate. C/20 for an 85 a/h battery is 4.25a = 51watts, whereas a 110a/h will be happy at 5.5a = 68watts. So if you want to maximise your battery life (both in usage and in years) go for the biggest one you can get in the box

Hi Dave,

Thanks for the data. I hadn't realised that lead acid batteries had the same problem as NiCad etc and needed smart chargers to get 100% charge. I was aware of 50% being the sensible lower limit which is why I thought 85Ah was possibly OK but from what you have said I will be going for the larger capacity.

I assume that the caravan charger is NOT a smart charger? Can't find anything in my manual to suggest that it is.

Thanks again