I have been replacing my 4d and 8d marine batteries with 2- 6volt golf cart batteries in series. I have found them in battery stores in Guaymas and if they don't have them in stock they can order them in for you. You might check with Costco in Hermosillo as well. I know the Costco stores in Arizona usually handle golf cart batteries. The golf cart batteries will do a great job as they will really take the deep cycling and recharging and the footprint is about the same for two of them as one 4d.