So with increased odds of a power failure (Irma) i got this $5.11 MPP gizmo ready to go.
I had no confidence that it can deliver 5a for any length of time, so i added a large heat sink and a 2" fan ($1). fan takes 2-3 watts. On a bench test, it does hold the input V wherever you set it, as long as it is range. Even with no load, it will keep the input cap happy. Say i set the MPP at 34v and have 37v, the cap sees 34v, that is pretty neat, since it has a cap rated only 35v.
Added a diode, as per instructions, to prevent backflow when hooked to the SLA's.
Irma may only deliver 55mph wind here in NSB, but it still could knock out power for 2 days, as they won't try to fix it until the storm has passed, and winds below 40mph. I doubt i will get to need it this time, as the storm is so big, i'm not sure the sun is still out there