Ok...I've decided on a split charge relay 'kit' with full instructions from eBay. Question: when the leisure battery is wired up, how do I wire the radio to it? Do I run a cable from battery to front of bus and find which is radio power wire and connect them?
Worth noting that some of the "instructions" I've seen tell you to connect the relay coil to a switched ignition feed. This is wrong: you need to trigger it from the alternator light output, or you'll be trying to start the engine from the leisure battery. Run a supply from the leisure battery to the front of the van (via a fuse). Worth putting an additional fusebox down the front (or rear). Your radio will likely need two feeds: one switched from the ignition, and one permanent 12V supply to maintain the radio station memories.
I guess if I go slowly slowly I can figure it out. Thanks. Electrics are all spaghetti to me at the moment but I'm determined to learn and wire up the battery, radio and phone charger and tidy it all up.
Had a poke and probe today. The alternator appears to be functioning okay, and the VSR is sending charge over to the leisure battery - but not at idle as there's not a high enough voltage to trigger the relay. Rev the engine (or just drive it!) and a good healthy 13v is going across. I'll keep an eye on it and see if it keeps draining quickly. It'll get a good run up to Techenders in a few weeks. Thanks @snotty and @mikedjames
Take the -ve lead off your leisure battery (so only starter battery's connected), start the engine and see what kind of voltage you get, measured at the battery (not up front). As Mr Westy says, at 13V, there's not going to be much charge going into the batteries.
I have all the interior lights/sink pump/shower wired to spare battery ,I don't like the thought of anything using my main starting battery...
