# Using a 12 volt battery charger to charge your 12v wild



## MrColt (Mar 15, 2009)

How would that work, is there a 12 volt charger you could buy that would plug on the cigarette lighter (12volt) socket, and run the leads to the back of the motorhome and hook them onto the habitational battery to charge. 

Would the engine need to be running? 

Could you use the vehicle battery to run the habitational area while charging? 


Thanks


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## DABurleigh (May 9, 2005)

You are picking a strange solution - it is not good practice to run down your vehicle battery for habitation purposes as the engine won't start.

Maybe if you described your requirements, we could point you to a better approach.

Dave


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## MrColt (Mar 15, 2009)

Well that leads us to our next question, how long would it take to charge it, we read somewhere that it would take around 2-3 hours to charge the habitational battery using the 12 volt battery charger.

IS that accurate, if so then the vehicle battery should be ok and not be totally flat.

Does that make sense?

We are wondering how to charge a battery (habitational) using a 12 volt charger when wild.

Thanks


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## MrColt (Mar 15, 2009)

Come to the chat room if you like.


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## cabby (May 14, 2005)

your choice is a solar panel, or a wind turbine.maybe have two leisure batteries.dont use uneccessary lights etc. is my advise.

cabby


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## gnscloz (Oct 4, 2008)

MrColt said:


> Well that leads us to our next question, how long would it take to charge it, we read somewhere that it would take around 2-3 hours to charge the habitational battery using the 12 volt battery charger.
> 
> IS that accurate, if so then the vehicle battery should be ok and not be totally flat.
> 
> ...


sterling battery to battery charger (needs engine running) or genny


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## DABurleigh (May 9, 2005)

If you are maximising lead acid battery life, you should not be repeatedly running down standard leisure batteries below 50% and you should not be charging them at a rate greater than a fifth of their capacity (so 20A for 100Ah, say).

Given Ohms law you don't average anything like maximum charge rate over the charge duration, and given charging losses, I'd say a rule of thumb for charge duration of standard leisure batteries is not less than 4-5 hours.

No, you are not making sense to me, but until you describe your requirements/ scenario, I'll guess we'll go on like ships passing in the night.

Dave


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## pippin (Nov 15, 2007)

If what the OP is suggesting works then he will have discovered the ever-elusive secret of perpetual motion.


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## MrColt (Mar 15, 2009)

DABurleigh said:


> If you are maximising lead acid battery life, you should not be repeatedly running down standard leisure batteries below 50% and you should not be charging them at a rate greater than a fifth of their capacity (so 20A for 100Ah, say).
> 
> Given Ohms law you don't average anything like maximum charge rate over the charge duration, and given charging losses, I'd say a rule of thumb for charge duration of standard leisure batteries is not less than 4-5 hours.
> 
> ...


We have already said, ....

We are wondering how to charge a battery (habitational) using a 12 volt charger when wild , and not using a hookup (240)

Without going into too much detail about ohms law and things alike, what is your experience with charging a habitational battery in the wild using a 12 volt battery charger, and how did you do it.

Thanks

Thanks


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## philoaks (Sep 2, 2008)

[/quote]

We have already said, ....

We are wondering how to charge a battery (habitational) using a 12 volt charger when wild , and not using a hookup (240)

Without going into too much detail about ohms law and things alike, what is your experience with charging a habitational battery in the wild using a 12 volt battery charger, and how did you do it.

Thanks

Thanks[/quote]

If you are wild camping with no hookup then to be able to charge your habitation battery then you need a power source.

As others have already mentioned, typically this could be a solar panel, a generator or running the vehicle engine. To make an informed decision on what would be the best option you would need to give some idea of the sort of wild camping that you will be doing. i.e. summer, winter, uk, europe, number of nights etc etc. There are so many variables that need to be considered!


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## DABurleigh (May 9, 2005)

"Without going into too much detail about ohms law and things alike, what is your experience with charging a habitational battery in the wild using a 12 volt battery charger, and how did you do it."

Right, once you dismiss confusing things such as cigarette
lighter socket with leads going back to leisure battery:

1) Sun power - solar cell, minimum 85 watts capacity or so. Pretty useless Oct to April if flat on roof.

2) Wind power. Forget it unless you fulltime parked next to yachts.

3) Hydrocarbon power. For £3-4k, a quiet methanol fuel cell. Noisy genny or run engine for hours. Perhaps drive to next night's spot using Sterling BtoB charger to top up if not TOO run down. 

Dave


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## grizzlyj (Oct 14, 2008)

Unless the OP is suggesting taking some power out of the starter battery having arrived at the nights camping spot, and recharging the leisure battery with it?

In which case all you are effectively doing is using all your vehicles battery capacity for habitation purposes once camped. The point of having leisure batteries is to ensure when you come to start the engine the following morning you have a fully charged starter. How will you know how much is too much if its left swapping/charging all night?

If you really really thought its a good idea, you'll still be losing energy via the charger. So why not use the same batteries for engine and leisure and just swap when you need to? You are still leaving yourself wide open to not being able to start the engine, and deep cycle leisure batteries aren't really suitable for high amperage starting duties. 
If you maintained the leisure battery nearly full charged and didn't ever discharge very much I personally don't see why the leisure would have to be a deep cycle and could be a starter type. I think very few people would agree though!


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## Counter552 (Jun 18, 2008)

MrColt said:


> How would that work, is there a 12 volt charger you could buy that would plug on the cigarette lighter (12volt) socket, and run the leads to the back of the motorhome and hook them onto the habitational battery to charge.
> 
> Would the engine need to be running?
> 
> ...


I think you have a sensible question, however, either a direct link from the vehicle battery or using a 12v charger from it to charge the habitation battery will run the vehicle battery down. You would be aswell with an additional habitation battery.

If you are wildcamping for more than 1 or 2 nights at a time, you would need to be using the vehicle to recharge both batteries or find a power source.

I bought a genny when we first got the Motorhome, but we have never used it. We can manage for a weekend on the habitation battery if we are careful with the use of lights etc, for longer trips we always use sites.

Hope this helps.


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## MrColt (Mar 15, 2009)

Counter552 said:


> MrColt said:
> 
> 
> > How would that work, is there a 12 volt charger you could buy that would plug on the cigarette lighter (12volt) socket, and run the leads to the back of the motorhome and hook them onto the habitational battery to charge.
> ...


thanks

sounds about right

We were only wondering in general if anyone had any experience ( in any enviroment for any number of nights), we didnt realise we had to be so specific with a general question, it wasn't supposed to be rocket science, only a question with no real direction.

We have a spare habitational battery, this was the idea behind the thinking.

Arrive at site, use habitational until it is nearly (not too near) flat for (as low as safely possible without damaging hte battery.

Take that battery off, put on the other habitational to use as main power source.

Use hte 12 volt habitational battery charger to charge the "flat habitational just taken off of the motorhome, the 12 volt battery charger comes with a "cigarette lighter connection that goes into the dash" so we would use that source (vehichle battery) to charge the flat habitational, but we were not sure because we didn't know how long you need to charge the habitational for using a vechile battery and not to mention flattening the vehicle battery too much.

This might work for two days, but obviously not a week or something like that as the vehicle battery would never get to fully recharge unless you run the engine.

Does this make sense to anyone.


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## joedenise (Jul 20, 2007)

Seeing as you have the extra battery couldn't you connect the two together all the time to save having to change them over - and no charger. Two batteries will easily last you for more than a weekend.

Joe


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## aultymer (Jun 20, 2006)

Mr Colt, since you need an explanation which does not involve Ohms law or indeed any sensible physics you need to look at your batteries as buckets of energy.
When you have drained all the usable energy from your habitation battery (bucket)you could use a 'thingy' plugged into your dashboard socket.
This 'thingy' will draw enough power from your starter battery(bucket) to recharge your habitation bucket but in doing so will have emptied the bucket of power needed to start your van when you want to move.
In other words, what you appear to want to do, WON'T WORK.


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## val33 (Jun 29, 2008)

Please don't take offence from any of the replies you have received, they are all trying to help, but it would seem that you have not really grasped how this battery malarky works.

In basic terms, you can not charge a battery from a battery. To recharge your liesure battery you need another power source. Either the engine alternator (which functions when you are driving the van), Mains Hook-up, solar panel or generator.

If you have a spare liesure battery, you really need to fit this in parallel with your existing one, that way you will have double the battery life. 

Hope that helps.

Val


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## 1302 (Apr 4, 2006)

....can I make wine from rain-water?

Please dont confuse me with any technical reasons why it wont work!

Thanks


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## karlb (Feb 22, 2009)

http://www.motorhomefacts.com/ftopic-89907-0.html


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## aultymer (Jun 20, 2006)

> ....can I make wine from rain-water?


Come on - that is so easy!
Add a bit of fermented grape juice to your rain water and you have wine - some producers have been selling us this stuff for years!


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## MrColt (Mar 15, 2009)

aultymer said:


> Mr Colt, since you need an explanation which does not involve Ohms law or indeed any sensible physics you need to look at your batteries as buckets of energy.
> When you have drained all the usable energy from your habitation battery (bucket)you could use a 'thingy' plugged into your dashboard socket.
> This 'thingy' will draw enough power from your starter battery(bucket) to recharge your habitation bucket but in doing so will have emptied the bucket of power needed to start your van when you want to move.
> In other words, what you appear to want to do, WON'T WORK.


I dont need anything pal. Im just asking if anyone has done such a thing before.

I understand how batterys work, and theoretically you can charge one battery from another, Im not syaing it wont flatten the battery you use to charge another one. But suprisingly you "gathered" from my question that I thought you could charge a habitational battery forever using a vehicle battery without flattening it .

You certainly havent understood what I meant, and i thought it nessecary to point that out.

"Thanks for your help" but instead of thinking about what im saying, your just stating the obvious.

I understand perfectly the ethics of using one battery to charge another, I was just grasping at straws for ideas as to how long you could push your luck doing so for.


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## Stanner (Aug 17, 2006)

If you connect two fully charged batteries and use the power that would have been in one of them, you just end up with two half charged (and therefore probably useless) batteries, don't you?


I.E. the water level in the two buckets will equalise at half full.

Does that answer your question?


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## 1302 (Apr 4, 2006)

MrColt said:


> I dont need anything pal.


Have you read this??

http://www.motorhomefacts.com/ftopic-89907.html

I think you are another one who's lost your 'polite license'

People are trying to help you but you are either:

a) struggling to put your point across
b) thick
c) rude
d) both b) and c)


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## MrColt (Mar 15, 2009)

1302 said:


> MrColt said:
> 
> 
> > I dont need anything pal.
> ...


I think it is you who has lost your polite license.

Do you for one minuite think it is me who has been rude?

You are someone who has also not read the whole thread properly.
I was making a reply to someone who was being rude. Some people have been helpful and they have received thanks.

So its you who is either

a) struggling to read the whle thread properly
b) thick
c) rude
d) all of a) b) and c)


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## MrColt (Mar 15, 2009)

Stanner said:


> If you connect two fully charged batteries and use the power that would have been in one of them, you just end up with two half charged (and therefore probably useless) batteries, don't you?
> 
> I.E. the water level in the two buckets will equalise at half full.
> 
> Does that answer your question?


Thanks for your reply.

Yes I understand that, thats not what im getting at, ,but thanks anyway.


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## raynipper (Aug 4, 2008)

Hello MrColt.
Many times using American motorhomes, both the chassis and habitation batteries were positioned in the same location. Either under the hood, step or beside the rear engine.

When leaving the motorhome in storage with a 'intelligent' charger connected to the engine battery. It was a simple matter to use a link, i.e. a short but heavy cable with crock clips on either end, to connect both sets of batteries together via the + terminals.

This would also work to distribute the remaining power from your engine battery to the house ones. But I am not sure your battery layout would accommodate this.

Ray.


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## Stanner (Aug 17, 2006)

MrColt said:


> Stanner said:
> 
> 
> > If you connect two fully charged batteries and use the power that would have been in one of them, you just end up with two half charged (and therefore probably useless) batteries, don't you?
> ...


Well sorry, but as others have pointed out you are not making very clear exactly what you do want to know and exactly what you do know about what you want to know about.

If you are asking if there is any magic device that will take power out of one battery and put it into another battery without flattening the first battery - there isn't.

So for the avoidance of doubt - if you draw power from a battery (or any number of batteries) sooner or later (dependent on the capacity of the said batteries) they will go flat unless an external source of power is supplied.


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## DABurleigh (May 9, 2005)

"what you do want to know and exactly what you do know about what you want to know about."

Clearly a Donald Rumsfeld fan  I always felt sorry for him for his infamous quote. It was accurate and pertinent, but he got vilified.

Dave


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## grizzlyj (Oct 14, 2008)

To my ears as soon as someone writes "pal" that hasn't previously it comes across as aggressive, as it seems to have with some others here?


So it would seem sensible for you to connect your spare one up more permanently than it is currently? My leisure batteries are wired in series to give 24volts. The compressor fridge, microwave when we had one, water pump and eberspacher are all 24v. Everything else runs on 12v on two circuits each with their own "dropper" from 24 to 12 volts. This loses at bit in the conversion, but is better than it was (a seperate circuit off each battery). 

If you wired the two you have in parallel as suggested you will obviously be using both at the same time and at 12v, without any reconnecting or voltage difficulties.


Someone who knows more than me, or Google, will tell you that when in use and also when charging, the "first" battery in the circuit will always age more quickly, ie one does more work than the other, but I can't remember which set up does that sorry


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## DABurleigh (May 9, 2005)

MrColt,

As Ray suggests, if you wish to explore using your vehicle battery to top-up your leisure batteries, this is simply done by a fused switch across the split-charge relay. No "charger" to buy or wiring to thread through the van. This page explains the approach:
http://www.motts.org/BRIDGING FUSE.htm

To mitigate the risk it might be a good idea to park next to someone friendly and have high-quality jump leads!

Dave


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