The criteria I had for SLA was all about Ah to weight. The older style SLA batteries, while cheap, also weigh a ton. I had considered AGM batteries which are SLA, but seem to have several advantages over conventional SLA batteries.

The obvious one is weight - a single 12V 26Ah AGM battery I looked at was 12 lbs compared to the 20+lb "conventional" SLA batteries of the same Ah rating. Second, AGM batteries seem to charge and draw at a higher rate, and leakage becomes less of an issue if the cells crack.

Once I priced everything out - including the charger, I found that the high end SLA's and LiFePO were so close in price that there isn't much of a saving...

The recent price drop of the LiFePO batteries caused me to rethink and I'm buying a 20Ah LiFePO pack and skipping the SLA stage. It just makes sense because I won't have to "tweak" anything, simply upgrade to the 40Ah cells once I have the BMS built and tested on the 20Ah cells.