Lead acid batteries cost about $100/kWh of nameplate capacity, more like $200/kWh of usable storage. At a 50% depth of discharge you're going to get about 1000 cycles out of the battery.
http://www.mpoweruk.com/images/dod.gif
So assuming 100% charge, discharge, charger and inverter efficiency (reality is more like 60% through that whole cycle) a person stands to make about $0.06 per kWh per cycle (in the UK anyhow) and they can only get 1000 cycles.
$0.06 * 1000 = $60 per kWh per battery lifetime
That's only 1/3 of the cost of the batteries, completely neglecting the capital cost of the charger and inverter and the time spent to set the whole thing up. Further, once you take the realizable efficiencies into account, it's more like $40 not $60 so they're losing money even faster.
This is a problem that -- at least for now -- LITERALLY solves itself.
