Sometimes comes the question, where and how to mount the battery to a trike.
The best place I found, is mounting the battery directly to the seat tubes, hanging low under the seat for enhanced cornering stability. The worst place for a heavy battery is on the rear rack, followed by mounting the battery on the front boom.
This is my DIY battery bracket. The right hand side bracket in this case, shown from both sides. Two half coupler mounted to a 100mm wide, 3mm thick aluminium plate.
My batteries are inside waterproof Ortlieb outer pockets size L.