Note that time honoured lead-acid starter batteries for cars work out about $200 per kwh, albeit shallow draw and clunky. But no pumps, easy recycling.

The addition of capacitors to standard lead acid batteries together with some over-capacity transforms the lifespan of lead acid, as it is deep discharge which damages them:
http://alfin2100.blogspot.com/2008/01/ultracapacitor-battery-hybrid-elec...