Linking two leisure batteries together

[gypo]

A friend of mind kindly gave me another leisure battery. Is worth linking the two together for when im wild camping?
Am i right in saying if i link plus to plus and neg to neg so in affect they will be parallel rather than inline as per the pic

Cheers
G
http://imageshack.us/photo/my-images/29/5t86.png/

[California Dreamin]

The picture IS parallel (keeps 12 volts but increases capacity for camping)...pos to pos & Neg to Neg but as the batteries are often located in two different places you would just give the second leisure battery a separate earth.
Charging two connected batteries of different capacities can sometimes lead to uneven charging, so my advice would be to disconnect and charge them independently every few months.

Martin

[gypo]

The picture IS parallel (keeps 12 volts but increases capacity for camping)...pos to pos & Neg to Neg but as the batteries are often located in two different places you would just give the second leisure battery a separate earth.
Charging two connected batteries of different capacities can sometimes lead to uneven charging, so my advice would be to disconnect and charge them independently every few months.

Martin

Thanks for the reply, one is 75ah and the other 85ah they would be right next to each other, i currently have a split charge relay charging the one, couldnt i just link the second to charge of this as well if they are next to each other?
Cheers
G

[California Dreamin]

I currently have a split charge relay charging the one, couldnt i just link the second to charge of this as well if they are next to each other?

As the second battery is directly connected to the first it will receive charge when the split charge system is closed (engine running).
The alternator just see's the two (actually three with the starter) batteries as one and this is where some inequality can occur (like I say, independently charge the batteries several times a year to ensure all reach 100% charge state)
Don't rely on your alternator to fully charge over 200ah worth of batteries. A large mains leisure battery charger may well be in order (10 amps plus) so you can plug this in a couple of days before you head out on a camp.

My next concern would be with the split charge circuit and whether it's man enough to charge 160 ah's worth of batteries...you need to check that the minimum rating of the circuit exceeds 50 amps (ball park figure) wiring/relay (fused around 40amps) obviously heavier is better.

Martin

[gypo]

I currently have a split charge relay charging the one, couldnt i just link the second to charge of this as well if they are next to each other?

As the second battery is directly connected to the first it will receive charge when the split charge system is closed (engine running).
The alternator just see's the two (actually three with the starter) batteries as one and this is where some inequality can occur (like I say, independently charge the batteries several times a year to ensure all reach 100% charge state)
Don't rely on your alternator to fully charge over 200ah worth of batteries. A large mains leisure battery charger may well be in order (10 amps plus) so you can plug this in a couple of days before you head out on a camp.

My next concern would be with the split charge circuit and whether it's man enough to charge 160 ah's worth of batteries...you need to check that the minimum rating of the circuit exceeds 50 amps (ball park figure) wiring/relay (fused around 40amps) obviously heavier is better.

Martin

Many thanks for the info. I understand what your saying, I might link it all up as per the diagram but put a simple battery isolation switch on the second one and just make sure it is charged before trips. Then when im traveling I can keep it disconnected from the alternator.

Thanks again
G

[nicq]

An isolation switch will not work because when the batts are connected together the fully charged one will charge the flatter one leveling them out. One way you can do it is to isolate the 2 leisure bats so that you can switch either bat on and run 2 split charge relays so they both charge. The advantage is dissimilar bats tend to flatten the better bat when connected together.

[ringo]

What are you running off your batteries?

I always advise to keep them separate. So for example, one battery for lights, water pump etc and then the other to supply the heater (propex/eber etc).
This way you avoid the batteries damaging each other or damaging them both at the same time (eg running them very flat). Too many times (twice) have I been in the situation where I've had no battery power and had a large bill to replace both. Now I find my batteries last longer and I also have the reassurance that I will still be warm if the kids leave the lights on etc.

Ringo