# Adding a second leisure battery



## duxdeluxe

I have a simple question here.... I need some advice on adding a second leisure battery.

The Original leisure battery is under the drivers seat. I have room under the passenger seat for another and was thinking of using the space (as we often spend a lot of time off hook up). The original battery is rated at 85 so I will get something similar size, but how to wire it up?

I know that it's -ve to -ve etc., but am looking for the following:

1) Do I need special cable or can I buy some jump leads and proper connectors and use the jump lead cable as cable, discarding the grips on the ends?
2) What size cable would be recommended? I thought about 25mm circ
3) Do I need a fuse between the two as they are not adjacent?
4) If so, what size fuse would be recommended?

Is there anything else I should be aware of?

Thanks in advance everyone

Have a good Easter Holiday


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## mark406

This is how Timberland have done it on my van.

1)Good quality 2 core TRS flex of 4mm2 cross sectional area. (TRS = Tough Rubber Sheath). Use readily obtainable Crimp Connectors to attach to the battery posts/terminals.

2)As above. 25mm2 is way overboard for the size of currents to be encountered here.

3)Yes. Fuse each one seperately and as close to the battery as poss.

4)Fuse each one at 20A. That gives you a theoretical 240 Watts worth of power available from each battery. In practice, you'd probably never get anywhere near that amount.

I think it's always been regarded as best practice when adding a second battery, to replace them both with identical make, capacity etc. irrespective of the condition of the original. (although finances will have a part to play on that decision... :roll: ) Just adding a new one next to an existing, albeit working battery, may not release full potential .

Both of mine (2x85Ah) are under the drivers and passengers seat.
Timberland say that you have to remove the complete seat to get access to them, but I've had them out to check them by just removing the plastic lower seat trims which just click into place. (Ducato base vehicle)

Don't forget to strap the second battery down under the seat!

Hope this helps.

Mark.


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## duxdeluxe

Thanks - much appreciated.

I'll order a couple of 85AH ones on line and get all the bits from various sources. Should be easy enough to fit - I hope!


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## duxdeluxe

Another question - looking around, some say use the thickest cable possible between the batteries..... others not. Is there any real reason for this?

Thanks.


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## pieterv

It is quite possible that the biggest current is going to be on charge, so you could have a look at the charging wiring going to your current battery, and have similar gauge to hook up the second battery.

Having said that, any voltage drop is bad, more so on charging than discharging, as a few tenths of a Volt can make a big difference. On my gel battery, 12.8V is full capacity, and it goes down in steps of 0.2V for each 25%. Charging voltages will obviously be higher, but of 0.1V drop in the wiring will reduce the max charge current considerably. So yes, bigger gauge is better.


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## mark406

duxdeluxe said:


> Another question - looking around, some say use the thickest cable possible between the batteries..... others not. Is there any real reason for this?


This is probably less to do with actual currents likely to be encountered during normal use, more to do with the cable's ability to handle fault current for the time it takes for the protection (ie the fuse) to operate in a short circuit situation. Not _so_ likely if it's been well installed.

Practically speaking, a larger cable is 'safer' although it will be physically more awkward to terminate the ends and fit fuses etc. in as much as anything larger than, say, 6mm2 will need a crimping tool bigger than most have lurking in their toolboxes.

The TRS cable I referred to above has a very resilient outer sheath and should not give any problems if you use it between the two batteries.

Mark.


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## DABurleigh

http://www.motts.org/second leisiure battery.htm


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## duxdeluxe

Thanks everyone....

I ordered two leisure batteries from Performance Leisure and they arrived at 0815 the following morning! cracking service and free delivery as well.

Ordered some cable from a vehicle electrical supplier together with the cable covering, fuses and clips etc. Some vent tubing from B&Q and battery carrier plus strap off fleabay.

It took about an hour to wire it all up +ve first and -ve last and test it. Now have double the capacity......

It'll be tested over the weekend - hope I did it all right - I followed all the advice. Total cost was about £130 including the two new batteries

Thanks again


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## gm6vxb

Check that your mains to 12 volt charger is up to the job. The Calira supply fitted to mine (from memory) is only for 40 to 150aH, so two time 110 aH would make it run hot, or kill it.

Martin.


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## duxdeluxe

Thanks - it should be OK


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