So, a final update. I took your collective advices and just picked up a new 3rd party battery (52v 14Ah).
I modified the rear battery rack and mounted the new module (which was supposed to be a down-tube water bottle mount) on to the existing battery tray. I decided to keep the existing tray...
Thanks guys.
I took a couple of quick measurements, and it will be a tight fit for the em3ev shark product... plus the crossbar with the water bottle bolts has a curve to it - so the battery pack probably wouldn't sit properly.
However, it shouldn't be too hard to just drill and tap a couple...
I have owned my Outlaw SS 3.5 since 2014 -- It only gets used a couple of times a week for about 15 miles each trip (mostly road travel, but a few bike/horse trails -- nothing seriously off road - this is a sooped-up commuter bike for me).
It got put into storage over the winter, since I...