Thats a fairly decent bit of DIY there, someone has far too much spare time on their hands

It's fairly basic control stuff there and it must weigh a stack with the lead contents, and have an incredibly short range without damaging the cells.
However electric-only will never be a solution for anything other than city driving, and it's the old long-tailpipe problem, the emissions are still emitted at the power station, plus extra for charge/discharge inefficiencies etc. There's a reason Toyota did a stack of tests on all-elec vehicles and concluded they were actually worse for well-to-wheel CO2 output than a standard economical Diesel. For a decent life on the cells you need to maintain charge nowhere near min or max and that severely limits your range, or means you need to tow a trailer full of cells! Or invent a new battery type.