Over the last ten years or so I have tried leisure batteries and car batteries.
I used to have a leisure battery and take it out to charge, bit of a pain.
What I now do is have a largish (770amp 85ah) car battery, I purchased 10mtrs of good battery cable online (ebay), got a friendly mechanic to wire the work battery in the back of the van so it charges while I drive, it has an isolator switch in he cab so I run the pump off the work battery and not the van so when I work a BIG day I do not ever run the risk of running down the van's battery.
I work 4 longish (10 or 11 hour) days each week and do some very large 10 hour jobs and the battery copes with them fine, being a car battery it is designed to recharge very quickly, and I only drive a maximum of 15-20 mins to go to work and the battery has sat in my van working all day every day for two years without any issue .
So I would buy the biggest car battery you can (they usually have a two year guarantee) and wire it up.
Like your previous poster you may have run the engine if you're very local to your work, but the recharge time on a car battery is very quick. Leisure batteries take longer to charge, so I prefer this way, over the last 14 years wfp it's the one that has worked best for me.
What I find so interesting is how different people have total opposite experiences with the same situation. At one time I to had considered using a starter battery as an auxillary battery.
The first van system I installed was for my son in a Peugeot Partner 800LX 53 plate. I fitted an 85 amp leisure battery under the passenger seat with a split charge relay. I also added a change over switch so if the leisure battery went flat he could continue by drawing current from the van's starter battery.
Son used to take his Jack Russell to work. This dog used to go mental at the sight of any person or dog who came close to the van. In one of her mental states she knocked the change over switch and son was unknowingly working from his starter battery. Within 4 days his starter battery was flat and wouldn't start the van to come home. He was parked on a hill and bump started it.
We also do very limited mileage a day, 20 to 30 minutes engine running time at the most.
The following year his starter battery had to be replaced, so I tried to run the pump off his battery again. It again lasted for 4 days before it was flat.
One of the windies down south had the same van, doing more mileage - engine running in congestion and traffic jams etc, and he only had his starter battery as his only power supply. He never charged his battery.
When son in law joined us a few years later he had a Transit Connect. We tried to run his pump directly from his starter battery. He also travelled further to work, albeit mostly motor way driving. His van battery was flat within the week. I had to jump start his van from my van with jumper cables. His van also used to do a lot more private mileage. For example they would drive out to his folks 30 miles round trip to have dinner and clean their windows.
I haven't been able to find any proof that a starter battery charges up faster than a leisure battery. So if you know where to find that info it would be very helpful. The new calcium batteries do charge quicker but they are designed differently and can handle much higher carrier voltage.
Webasto make engine preheaters and are very common in vehicles supplied into cold countries.
At one time, their Thermo Top C was the preferred furnace for this application. The heater is used to heat up engine coolant and defrost the internal windscreen and warm the cabin. It was recommended that the heater required about 30 minutes to perform this task. To begin with the diesel heater will draw about 20 amps in short bursts for around 3 minutes to get the heater fired up and fully burning. It then runs on about 2.5 amps. The recommendation by Webasto is to ensure your car journey is as long as your engine preheater had worked for to keep the battery charged up.
If the Webasto drew 20 amps for 3 minutes and ran for 27 minutes at 2.5 amps, the heater would draw less than 2.5 amps in 30 minutes. So Webasto are asking that the car/vehicle run for 30 minutes to replace the current the preheater drew. That sounds similar to leisure battery charging specs to me.
ATM P&F is just managing to break even with his solar panel charging setup. Even if he had a starter battery and it did charge faster than a leisure battery, it wouldn't make much difference to him as the problem is the panel wouldn't keep up with power consumption, especially during the darker winter days with limited sun.
My problem is that as a twin operator van, those solar panels will not be suppling anywhere near enough power for my daily consumption now because I probably use twice the amount Rich does. So my solar array on the roof of my van would need to be around 250 watts to supply my Autumn needs. Winter - well we wait to see how Rich's system performs.
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