Sur-Ron is roughly 2kWh. If both it and sons battery were completely dead (highly unlikely), I can recharge both off the house batteries once. When we ride on weekends that will be plenty. Van has all week to recharge if I don't drive it. At an equivalent 3.5hrs/day peak average around here thats about 2 days. I haven't picked a B2B charger yet but, yes, the alternator will also charge the battieries on the ride home, to work, etc. No, ecus don't change the idle speed. FWIW, I didn't actually size any of the system for running the e-bikes. It was mostly for flying RC planes and occasional camping. The 5.5Ah 6S flight packs are about 0.1kWh. I have planes that take 1, 2, or even 4. In the electric jets those are good for ~4min of flight. There is enough storage to let me fly as much as I want the couple days a week I get out. Driving to/from the RC field and office would easily recharge them. The solar is just convenience and speed of topping it up. W/ a 2kW inverter I'm tempted to even try a portable room AC in the van to use when sleeping. Would encourage camping on hotter weekends. Even 5C difference and dropping the humidity greatly improves sleeping. Having decent electric power anywhere you go changes the way you look at things. A small microwave is next... I've worked in the off-grid solar industry for 20yrs now so am well versed in what it can (and can't) do.