I have a small canvas shop, so I made up some velcro straps and closed cell foam pads so I can stuff my battery into the hatch and velcro strap it to my skuppers so my battery cant move. But I could do the same thing with some rope, etc...
On my wifes yak, I made a foam triangle to keep the battery centered as her boat has a definate V shape, but again I sewed up velcro staps to hold the battery in place...
Works great!
I also smear dialectric grease on all connections like toothpaste on a brush, and then clean/ re- do every 8-10 trips...
No problems so far...
Cowboybill