This is version 1 of my battery box with mounting brackets, the battery is 110mm x 95mm x 220mm so the case is in three sections. The bottom bracket has a lid to keep the weather out and I painted the case with a few coats to make it water tight.
Due to the size and the need for strength this will take a whole roll of filament if you decide to use it.
It's not very elegant I'm afraid so maybe someone a bit more arty can make it more attractive.
The bike mount is from an old bottle battery.