Those UB12350 batteries work pretty good. At one point, Optima had their 6v batteries on national back order, so I asked my battery vendor what he recommended and he said the UB12350. The fit the Shelby and Kirkham trays nicely. The Shelby tray is longer, so there is some space between the batteries. They use those UB12350's as a battery backup in slot machines, so my local battery shop has literally 100's of them in stock.
Here I thought I was being brainy by finding them, but Kirkham had them in their sites all along.
