There is lots of point in carrying batteries that can only be half discharged, almost everyone with a motorhome or caravan across the world does exactly that, it's down to cost, simplicity and convenience.
Lead acid batteries are still in use because they work, if your worried about carrying a battery a sealed gel type lead acid battery (such as an Optima or whatever) could be stuffed in the bottom of a rucksack along with a cheapy smart charger and plugged in for the day, plus you get a free workout lugging it about.
There is no doubt the more modern batteries are lighter and provide more output or stay charged longer, but they are much more expensive and require more expensive charging systems, you don't have to worry about balancing out cells, making up packs, making sure your van is set up for them or the fact most people wont be interested in buying avan with a weird battery set up in it after you finish with it.
A cheap battery you kill in a year or two is often a better investment than a much more expensive one that still may only last 4 or 5, my lead acid 90ah sealed leisure battery was less than 40 quid delivered, I can't see why you'd need to complicate things for a cheap van that will be used for a couple of years, I could buy three or four of them for the price of anything else and they don't need any "mollycoddling" at that price point.
Not that I'm saying don't check out all options of course, but the old ones shouldn't be dismissed just for being old.