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Battery - Charging Times

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Our Bailey Unicorn Valencia had the battery quite reduced in output after a long session at the dealers sorting and testing the mover. This resulted in the new 100Ah Duracell battery showing 10V at the end of the last weekend of use (no EHU which most of our sites don't have) and being unable to power the mover when we got home.


I have a 6v/12v Hi/Lo charger (Streetwize) 8A RMS.


There seems to be lots of conflicting advice about how long to charge the battery for. I overcharged the old battery and boiled it dry and now have the new Duracell battery and am paranoid.


How long should I charge the battery for from the mains, and at what setting?


If there is a relevant thread, can someone please direct me?



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After being pulled down to 10V that battery will have a significantly shorter life but with any luck still has a few months left in it.


To fully recharge it will probably take something like 36 hours but check to see if it's getting hot during that time. Warm is okay but hot indicates a faulty cell and batteries can (and do) go bang when on charge with a faulty cell. Keep the cells topped-up during charging if it's not a maintenance-free unit.


The only true way to quickly check the state of charge is with a hydrometer. Again, only if it's not a sealed battery.



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The usual rule is Ah/charge current +10%.


This if your battery is 100Ah and your charger can output 8A then it would take 1. 1(100/8) or about 14 hours. However what current does your charger actually output given that it is d. c. but the current available is shown in RMS which is an a. c. measurement? Best thing to use would be an ammeter so that you know exactly what is going in.

2018 Passat B8 Estate 150GT TDi150 towing a 2018 Bailey Unicorn S4 Seville

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The usual rule is Ah/charge current +10%....

And the usual rule is wrong for all but the smallest chargers.


The battery will self-limit the charge current as its internal resistance rises along with the charge status. So if you had for example a 40A charger it would only supply 40A to the battery for a very short time, if at all, making the above rule meaningless.


It also depends on how flat the battery is - has it delivered 10Ah? 20Ah? More? The more it has delivered the more has to be replaced and the longer that will take. In the case of the OP it has delivered 95% of its capacity and will never recover from that. It's probably now only an 80Ah battery.


The final stage of the charging curve takes an awfully long time - much longer than many folk appreciate - and this is why you often see quoted that a caravan PSU will only charge a battery to 80%. That's rubbish. It will charge the battery to 100% but it won't do it in a few hours.



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Best to charge the battery with low amps over a long period ie. 24 - 36 hours.

If yours is not a smart charger, CTEK or equivalent, then you really need a cheap multimeter to check the progression of the charge. If after 12 hours the voltage is still around 14. 4 volts then you are running the risk of boiling the battery, so best disconnect and let the battery settle for a couple of hours. Ideally the final voltage with charger connected should be about 13. 5 volts.

Edited by onewheelonmywagon

Land Rover is now back towing.

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Thanks. Never got to grips with electrical issues!


The charger says 6A dc when set to low. Battery is maintenance free sealed type.


We seem to have had nothing but trouble with batteries on this caravan. This one has only been used 2 or 3 weekends.


We use the 'van about every 3-4 weeks over the summer and autumn (April to October), at sites with no EHU, but are generally only using electricity in the later evening for an hour or so as we are outside most of the day and evening. Lights and pump only, no TV or anything. Motor mover is rarely used.


The car journeys can be quite long - c. 100 miles+ but don't seem to contribute to keeping the battery topped up.


Caravan lives away from the house. What is the best way to keep it topped up and going? (though TonyJ implies its kaput)


Would a solar panel help, and is it ok top leave it connected all the time when the van is stored and the panel is placed in a window or in the roof light say? No danger of over cooking the battery?

Edited by Simon_Sue
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Hiya. Well, the reason you've had so many battery problems is that you abuse the battery - no offence intended.


Lead-acid batteries like to be kept fully charged. They HATE to be allowed to self-discharge, especially down to below 12. 2V.


Yes, solar would help you enormously. A small panel won't damage the battery but your best solution would be a larger panel (40W or bigger) charging the battery through a small charge controller. The larger panel will help through the winter months, and the charge controller means that it won't boil the battery.


A 2 or 3 hour car journey will never put much of a charge into a battery, but it will help if you're sure that the charging circuit is actually wired on your car socket.


Good luck,



Or of course, you could take the battery home and keep it charged there.

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I think I have abused it.


Was at the local caravan place yesterday. They said that my charger was a smart one, and that the new Duracell battery we have will take discharging. We also bought a 40W solar panel which has a built in charge controller. ......


Lets see what happens!


Thanks for the comments and advice.

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