So, I figured there are 3 sources of charging available on the road - Alternator, Solar, and 240v hook-up.
Each needs to be regulated so the batteries get the optimum charge (apparently 14.7V for AGM). The solar, producing 17+V needs to be managed and the best tech is called MPPT or maximum power point tracking and is a DC to DC converter that makes the most of the available charge.
I think my alternator will make about 75A at around 14-15v and although I'm not planning on ever piping 240v directly to sockets in the van, it can be used to charge the batteries, just like you would at home with a trickle-charger.
So you need an MPPT, a transformer for the 240v as well as the alternator. And then you have to work out how all that is going to charge the batteries. You could have a series of switches but that's a real ball-ache and frankly I know I'd forget to turn them from one to the other and then get confused and it would all go horribly wrong. And they have those huge panels that just look scary & ugly so I wanted to avoid those too.
It's relatively easy to get the alternator and solar via the MPPT to charge the batteries, but adding in the option to automatically switch to 240v charging wasn't as easy.
Infact it was a total nightmare. How do you get them to switch to the most efficient source? Or even multiple sources? Flipping hours I spent on this, even researching marine forums as boats and buses have a similar set of needs and options. It all came back to needing to flip a switch sometime.
So I called Tim (Impmad 2000) all round top bloke and electrical guru.... "Check out CTEK he said - haven't used them, but they have kit that I think might do what you're looking for."
And so I did. Genius. Swedish company and they have something called a 'Smartpass' which links to their version of an MPPT and can be combined with Alternator charging and one of their 240v battery chargers. And no switches needed. It's all done in the smartpass...and if there's a surplus of electricity, it will then top up your starter battery automatically too. Brilliant.
Even better, it has temperature sensors, so will reduce the current into the batteries if it gets too hot....
Frankly, I think it's witchcraft, but this is how it is set up:
And if you're really keen, here's 3m 45s of your life you'll never get back (no sound...)
https://www.youtube.com/watch?v=aN6oF-wj9XQ
And finally, for those 240v needs like laptop and camera batteries, I've gone for a portable 300w pure sine-wave invertor, which of course steps the 12v DC back up to 240v AC. So called pure sine wave, because it has the classic sine curve of AC power that we know and love from our school maths. Other invertors can alternate the current, but do so cheaply by making a square wave - this can damage laptops and stuff, so I avoided those.
This one will plug into a cigarette lighter that will have a fat 30A fuse fitted to it, so we can get the full 300w out of this - otherwise, a standard 10A fuse would mean the draw would be only around 100w. Apparently.
So there you go. The product of about 2 months of research and choices. But it means I'll have really flexible, really automatic, really fit and forget electricity for the bus.