# 2nd battery



## carprus (Jun 22, 2008)

Hi , I have 1 85 amp battery in the rear , but would like to add another alongside .

The one I have is charged via a split relay , with just a single wire to the live side , what I would like to know is how do I wire up the second battery. :wink:


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## peedee (May 10, 2005)

Connect the live of the second battery to the live of the original and the neutral of the second battery, which I assume is negative, to the chassis. (earth)

peedee


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## CliveMott (Mar 10, 2008)

Look here
http://www.motts.dsl.pipex.com/second leisiure battery.htm

.


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## TR5 (Jun 6, 2007)

One point not already made, is the size of the wires.
The greater distance between the batteries being linked, the greater size cable should be used, to avoid voltage drop.

If batteries are in very close proximity, I would suggest that 6mm would suffice. If more than a metre in length, then 10mm would be advisable.


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## carprus (Jun 22, 2008)

Thanks chaps , they are right next door to each other, so option 1 looks good , where I have a single wire from front to back at present from split relay do I just extend that to my second leisure battery? :?


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## TR5 (Jun 6, 2007)

Just wire the two together, positive to positive, negative to negative, using 4mm single multi-strand cable. A crimped-on ring terminal at each end will make a good connection.
If you don't have the necessary, a local auto-electrician will have.


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## 104817 (May 29, 2007)

I could be wrong but I'm sure I recall a thread somewhere advising fitting a fuse inline between the two battery positives. Unfortunately I can't remember where the thread was or why you'd do it! Perhaps it was to safeguard the split charge against overcurrent or something if both batteries are very or fully discharged?

Phil


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## 104817 (May 29, 2007)

...wish I'd clicked that link before I posted my first reply....


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## TR5 (Jun 6, 2007)

vanner said:


> I could be wrong but I'm sure I recall a thread somewhere advising fitting a fuse inline between the two battery positives. Unfortunately I can't remember where the thread was or why you'd do it! Perhaps it was to safeguard the split charge against overcurrent or something if both batteries are very or fully discharged?
> 
> Phil


You only require a fuse between the batteries if they are not in close proximity of each other, to protect the cables if they got damaged. Personally, if there was a long cable between the batteries, I would fit a fuse at both ends of the live, so that they would both blow if the cable was damaged, thereby isolating and protecting the cable. That's the only reason I know of!


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## 88879 (May 10, 2005)

Hi,i think i remember someone on here saying that both batteries should also be the same age & size due to a stronger battery pulling charge from a weaker battery.If i'm wrong i'm sure someone will be on here to shoot me down! Regards,Kafriz


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## trevorf (May 16, 2005)

> Hi,i think i remember someone on here saying that both batteries should also be the same age & size due to a stronger battery pulling charge from a weaker battery.If i'm wrong i'm sure someone will be on here to shoot me down! Regards,Kafriz


No need to shoot you down, you are correct 

Batteries of different age/type will still work together, its just that you will get greater efficiency from 2 of the same age and type.

Trevor


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## 107166 (Sep 22, 2007)

I,m just about to replace my 145 amp gel with 3 110amp sealed.

I know I need to link Pos to Pos and Neg to Neg. Will used 6 mill wire.

Are there any issues with the size of wire from the first battery into the system. 

i will change the charge mod to suit batteries.

If all OK I will have a 1 year old 145 amp hour Battery for sale

David


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## trevorf (May 16, 2005)

Depends on what you intend to run off it. 6mm cable is OK for up to roughly 5-600 Watts at 12V ie about 50 amps. If you plan to add a large inverter to run, say a 230V hairdryer then you will need substantially larger cables.

Trevor


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## 107166 (Sep 22, 2007)

At the moment the 145 amp battery goes to an inverter that is about 2 to 3 foot from the battery. (I,m not sure how many watts the inverter has but its German and big) 

The leads then go to the mains and distribution block. This unit has an additional charger rated at 16 amps.


By increasing the battery power to 3 x 110 amps will that require heavier cable. 

It will be easy to increase the cable size between the batteries and on to the inverter.

If the cable to the Dist Block needs to be changed I may need to borrow a small child. :lol:


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## Jean-Luc (Jul 21, 2005)

David, before you commit to the three sealed why not check out ordinary leisure batteries of the wet type where you can open the tops and check the electrolyte levels on conjunction with a battery to battery charger. 
This will give you a system with up to 50% more usable charge at the end of a run as the BtoB charger will push the charge up to 14.8 volts. This level of charging will cause some water loss so you MUST check the levels regularly, hence the recommendation for open type batteries, which incidentally are usually the cheapest.
Colin


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## 107166 (Sep 22, 2007)

Thanks for that.

I think the system that is fitted charges at 14.8 for a short while then drops down.

Not over keen on open batteries as they are fitted towards the back in the middle.

I still need to check size of cable !!

David


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## trevorf (May 16, 2005)

It does not matter how big or how many batteries you have. Its the current you draw from them that is important for cable size. Still the same for your inverter. You can have a 2000W inverter but if you only use it to charge your mobile phone then you will draw very little current.

If at all worried, then just use the largest cables that you can physically connect to the terminals.

Trevor


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## TR5 (Jun 6, 2007)

If you are not increasing the load, but using the additional amp/hr to extend the life of the battery power between charges, then the existing cable is sufficient (assuming it serves all your requirements efficiently prior to fitting the new batteries).

If however you intend to draw a greater load, then you will need to work out the maximum load at any one time, and the length of cable used to serve that load. This may/will require increasing the cable size accordingingly. Don't forget that you may also need to increase the negative (earth) cable also, to the chassis.


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## webfoot (Jun 9, 2008)

I am hoping to fit a second habitation battery to my new McLouis Steel 654 but have been advised by the dealer that rather that connect the second battery as normal, Iwould need to fit a change over switch so that only one battery can be charged at a time. Apparently the on board charger will burn out if you try to charge both batteries simultaneously. How can this be? Does the charger not just take longer to charge up two 85AH batteries, or am I talking rubbish. Feedback please


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## TR5 (Jun 6, 2007)

I can't see why a change-over switch would be necessary, as you say the charger will just take longer to charge up two batteries.
Two 1/4 discharged batteries will ask for no more than one 1/2 discharged battery - hope this makes sense.
In any case, all electical supply and equipment SHOULD be protected by adequate fusing..........????

Unless there is something particularly unusual with your vehicle, it sounds a strange requirement. Why not check with the manufacturer, just for peace of mind.
My MH originally had 1 x 85amp/hr and now has 235amp/hr being charged from the same unit.


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## webfoot (Jun 9, 2008)

Thanks for that. Yes I will contact the manufacturer, and I have already made up the nec essary wiring with 20amp fuse protection


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## Spacerunner (Mar 18, 2006)

Halfords sell ready made starter battery cables in various lengths. These should be robust for most applications.


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