The two 6 VDC, 4.5 Ah SLA's in my Springer are mounted on their sides, short side down, and up against the sides of the hull. The are on plywood platforms right at the belly of the hull, and are held in place by 2" squares of Velcro. In 3 years of running the boat the batteries have never shifted, even though I use the "Springer toss" method of launching every time. The platforms are long enough to allow 2 inches of fore-and-aft adjustment, to balance the boat fore and aft. A number of my Springer friends use a similar arrangement.
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