Has anybody used one of these?
https://www.ebay.co.uk/itm/CAMPER-V...e=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649
It's purely to keep a leisure battery charged........no winches, spotlights or 1000w sound systems so don't need to pay a fortune. Came across this and thought it looked ok.
I have used those made by Ring but the last one I got only lasted a few weeks then packed up. Having said that I got one on the series for 10 years + and still going strong but they are a bit flimsy so thought I might try one of these.

I use the Durite 140A for around £36. Its only a few £ more and Durite are very helpful, you get a real person! Also 30A is not much, the alternator can push 70A and there's a chance a lot goes to the 2nd batt if its been run down when you first start. That 140A gives you a margin for current flows from one battery to the other, bear in mind they sense across both batteries so the current flow can be either way. Mine is wired with 70A cable and fused at 50A Blown fuse once. The split cicuit is fused both ends in case it chafes/shorts as its got a battery on both ends and we don't want a fire while we're asleep. I run 50W solar permanently (fixed on roof) on the leisure batt with a 200w addtional (mobile to face sun) when parked. This means the flow is often from the leisure batt to the starter batt when parked.

I have just installed a split charge system in my S3 (mainly to power external lights and with an inverter for occasional power tools around the farm). Went for the T max kit sourced from Craddocks - obviously more expensive at £90 than just a relay (although I think they do a straightforward 200A relay for £30 ish) but it has the control box with display function showing levels of charge in both batteries plus the ability to link both if the starter one goes flat for whatever reason. Kit come with plenty of cable to take battery to seatbox plus all the crimps, ring fittings, plugs etc.
https://www.johncraddockltd.co.uk/ba2685-auxiliary-split-charge-dual-battery-system.html
Seems to work well and was straightforward to install apart from siting the battery as had to drop the floor of the seatbox to fit the battery in but that's hardly the fault of the kit. (PS. If you decide to go for the under seat location let me know and I can send links to a site I found who do replacment seatbox floors specifically for lowering them - guess who found the site after he'd already spent several wasted hours making his own from scrap steel in the workshop!!)

Cheers.Ian

Sorry - should also have said in post above that this is not suitable for AGM batteries or any of the fancier new types apparently - advised by my battery supplier that these type of relays will only work with lead acid batteries. Happy to stand corrected if someone else knows better as I'm no expert mind you.

I paid a tenner for mine. No probs for the last few years but went for a breaker instead of a fuse.
Think mine is 120 or 140 amp but it wasn’t advertised as a split charge anything so came in at around half price.

I like your facility to boost the start of the leisure batt. I was looking at the boat swiches that take a few hundred amps and have 1,2, both for starting. Bit of an overkill but could come in handy if wild camping! I've had a lot of issues with poor leisure batt capacity and was looking at AGMs and Lithium, and came to the same conclusion, really expensive, complicated and may not even work. Best think I did was put a cheap (£30) solar panel on the roof with a £10 controller permanenly connected. Now the leisure batt sits at 100% all the time, before it was usually between 80-90% no matter what I did.

I think the AGM and or lithium ones need a DC to DC charge system to work properly which are more expensive - there are loads of good youtube videos explaining the pros and cons and what you need for each type but like you I came to the conclusion that keeping it simple was best for the relatively limited range of uses I was going to put it to - plus it's an S3, don't want to get too fancy!!. I could probably have sourced a cheap relay and all the wiring bits for a lot less but I liked the idea of the dashboard display showing the charge levels of both batteries and the ability to boost the starter battery if required. I installed it to feed a 110Ah leisure battery and a 2000w pure sine inverter (planned for a 1000w one initially but the deal was good on the larger one although I suspect I would need rather more battery capacity to ever use most of the 2000W) - runs all the power tools I have tried so far including heavy duty 4" angle grinder etc. I was advised by an electrical engineer friend that proper fusing or breakers would be advisable so have added them to the circuit as well just to be sure. Just for info I have used a company called AES at autoelectricsupplies.co.uk for most of the extra cabling, fusing and switching etc required for adding the inverter and been very happy with the service)
Cheers.Ian

I decided against that one and rescued a 70A relay from an old camper. Ordered some 10mm cable and a couple of 30A fuses........that should do the trick I think, like I said its not a heavy duty circuit but a few extra amps might be handy one day.

I spent a lot of time looking at the 240v issue. I went for 12v but carry a small inverter which so far has only been used once. We do carry a DC-DC charger so the plan is we could recharge cordless tools and models/toys. I put in a mains hook up and fuse box, but installed it as a double insulated system entirely separate from the vehile. Electrically its like an exstention lead with the end inside (got advice from certified elect). I did this because the camper guidance is based on firbreglass / wood bodies not metal ones. When I looked into it the biggest risk was the campsite earth going live becuase some other idiot had plugged in a cross connected lead or a lead had got damaged and in the metal Series we'd be in trouble so we have all the earths isolated and double insutated appliances.

I would get a generic caravan relay for the towbar and use one of the switched contacts on this to switch a more substantial relay which links the batteries. Fuses on each battery's positive as power could be going in either direction. Use the towbar relay's outputs for their intended purpose as well and wire it to a 12S or 13-pin socket. I used mine as a charging point to keep the landy battery topped up- put a grey plug on the end of a battery charger and just plug it in.