i was wondering if this would be of use to me as i dont do that much milage. Does any one know how long you would need to keep the van running to charge the battery? thanks 
On a thread that is linked to this, Ian Sheppard made the following observation:
"............ if you take 4-5 amps for 5-6 hours in a working day but spend only 2-3 hours driving (and charging via the split relay) you will not put back in, what you have taken out."
This is also what we have found in practice. In Ian's example, a fully charged perfectly performing leisure battery would have 24 amps removed from it if the pump drew a constant 4 amps for 6 hours. So if you have an 85 amp battery it would only have 61 amps left in the battery.
Now, if you could charge your leisure battery at 10 amps you would need to drive for 2 1/2 hours to recharge that battery.
However, the only thing these figures tell you is that you have to do a lot of mileage to forget about bench charging your leisure battery. Charging and discharging of leisure batteries have so many different variables, its actually becomes a very complex procedure.
My son in law has a Ford Transit Connect with a Numax 85 amp h battery which is a few months old. He has a Varistream and a Shurflo pump. I charge his battery every couple of days with a Numax 10 amp intelligent charger. On several occassions he has come back at the end of the day and I have put the charger onto his battery and the Numax guage says its half capacity. He then drives 9 miles home and returns the next morning, having driven 18 miles altogether. His battery now will show that its has a 75% charge on my Numax charger. But the other day the weather was too cold to work and so he drove home again and back a couple of days later. But his battery wasn't fully charged, because the charge a battery will accept gets less as the battery gets more fully charged. It also performs differently as the temperature changes.
We have had split charge relays on 4 vans so far and all needed supplementary charging every couple of days as we do minimal mileage per day. On my van I have a 15amp fuse between the van battery and the leisure battery and in 5 years this fuse has never blown, which means that even when the leisure battery was very flat on a couple of occassions, the battery never accepted a charge of more than 15 amps as the fuse would have blown if it did. In fact, I have never replaced a single inline fuse in any of the vans yet.
On one occassion when the battery was flat after we were half way through a job, we had to start the van's engine and let the alternator supply the current for both pumps so we could finish the job. As that battery was nearly four years old, I ordered a replacement on our way home that day. That day was when a split charge relay really paid for itself. If we didn't have one, we would have had to return to the job the following day with a new battery - for us that was a saving of half a day and a round trip of 25 miles.
That is why I will always recommend a split charge relay, even if you do a low mileage - its a great backup.
On my son's van we have also incorporated a change over switch so his pump can draw from either the vans battery or the leisure battery. Although I bought another change over switch to adapt my van, I've never fitted it.
Spruce
