Yup, exactly what I was going to do - and they went down in price in the last few days. Noticed them today at 10% less than I thought was a good price. Made me rethink the whole SLA first approach. Think I'll buy them first with the necessary cables to make em into a pack ang get the cell monitors as well. Then I'll build out the BMS, attach them to it and then upgrade to the 40 Ah cells.

It's funny, but unless you go really cheap on the SLA's, you can have a 36V 20Ah L1FePO or 36V 26Ah SLA (both with charger) for about the same cost, with significant weight advantages to the LiFePO. Granted, I "upped" the SLA charger to a dual 20A unit, I figured it as necessary compared to the 3.3 h of the L1FePO charging unit. Giving that "step" up saved me about $700 on the overall budget, cutting two weeks off the timeline.

I also managed to find a 110+lb trailer with the hitch I want at the same price as my original spec, so the weight of the 40 Ah setup isn't a problem.