Sub amp modules?

I have no experience running things from batteries but... :)

You might try a TC2000 + STA517B board:
41Hz Audio:AMP11-HV kit (50V)
Hifimediy (T3)

Or I think (not sure) you could use 2x 24V batteries in series with gnd at center to provide +-24V and use this one bridged:
Undervoltage protection is at 23V, you might have to ask Cristi whether it would work.

None of these options will get you anywhere near 200W into 8ohms though. You'll need a lower impedance driver, or a step-up voltage transformer.