Hi John, It really sounds to me like 3 things alot easier than redesigning the Sparrow to accept different batteries could allow it to better satisfy your needs.
1st, is to come up with a way to turn down the amps on your charger, or create a small and inexpensive charger that wouldn't pop the ferry fuse. A little charge boost on the way home would go along way to helping you up that hill. Two, is to heat the batteries. I would think that 90F to 100F would be about right, as your regular use is going to cycle them to death before they sit around and rot. Three, something to kick your charger back on shortly before you leave so that you start your commute in the morning with a pack bouncing ready to go. I think this is the least important so long as your pack is getting well charged each night. Neon
