Planning an electric mower deck.

You might consider using the motors from a Black and Decker CMM1200 cordless mower. They're designed to spin a 19" blade, which should be pretty close for your application. They're not too expensive (as motors go) and they're readily available on Dewalt Service Net. Click the CMM1200 link for the exploded parts diagram. Heck, if your deck will clear the 19" blades, you could buy the entire blade mechanism that bolts to the motor spindle.

I have a CMM1000, which uses the same motor. It'll run 45-60 minutes on a full charge doing typical residential duties. The battery is a series-pair of 12V12 SLAs.

Thanks Grainman, I already have one of those mowers, & had thought about putting it on the deck, I will try and find another over the winter, as we travel the southlands in the warm.
I also have a line on used Golf cart batts which I can desulfate and use for power, I think a knife switch will be enough to get them going. Min cost that way.
Cheers.