if i remember correctly wasn't it the previous owner you bought it from who installed his own hatch/
Yes, he went thru 2 sets of sealed batteries and decided if he was going to burn thru batteries, he might as well burn cheap ones. The van has deep cycle lead acid vented batteries that need watering occasionally. Not practical if you have to unbolt 'em and jack 'em down every couple of months.
The way SMB does it seem like short term expediency for something that someone else will be stuck trying to maintain. If a battery set had the service life of a transmission or radiator it would be ok, but for something with about the lifespan of a set of tires - no.
In their defense - there is probably some safety reg about having hydrogen spewing batteries accessible to an enclosed living space.