Rechargable. (That's the whole point.)
You can also use it as a "DC Transformer". The cells all share a pair of circulation systems, one for the positive-plate solution, one for the negative. You can charge at one voltage and current, discharge at another, without changing connections - just put a bunch in series and connect the charging and discharging taps at the appropriate voltage levels. And you can do both at the same time, so it acts like an autotransformer. (Current through the cells between the lower tap and the common (ground) end is the sum of the signed currents (which means the difference if one is charging and the other discharging), current through the cells between the taps is the current through the higher tap.
How'd you like to charge your cells at 48V and discharge them at 120 DC for some loads, 12V for others, without any cell-balancing issues? Or adjust the charging tap automatically to get the most out of your mill in varying wind conditions? Or make a modified-sine inverter out of four switching transistors and a little control electronics? (Or a pure-sine inverter out of a bunch of transistors and a little control electronics?)