What type of batteries are we talking about? I recommend against straps, although I have used them. A bar across the top, with long threaded bolts or similar in each end of the bar. Not unlike how a battery holding in many cars works. The battery should not be allowed to move at all, and whatever form of securing needs to be able to hold it if the boat is inverted.
For an LFP battery built from cells, usually there is some sort of compression frame, and in the construction of that frame you can add brackets, such that the battery just bolts down to where ever it is.
If the battery is FLA, you need to contain the acid in a box that is not damaged by acid. That is more difficult to do than it sounds. A wooden box that is fiberglass on the inside works. And they sell plastic boxes that "work" but it is quite difficult to secure the batter such that it can't move. You are more or less restricted to using straps. Use big strong straps with metal brackets. Don't use the straps that come with the plastic box, which are useless.
