I have a yak power battery box for sale.
Waterproof "pelican style" drybox with:

Capacity for 3 SLC batteries
Onboard charger
USB ports for charging Phones,running lights or cameras
On/Off switch for power conservation
Pre Wired, Plug and Play

Here is a Link:
YP-BBK Power Pack Battery Box | Yak Power

Bought new last year $99
Will sell for $75. Buyer pays shipping

I bought this to power my fishfinder on my kayak. The box works great,but, I went with a different option for power this year.
PM me for any questions