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I'd love to use lithium but I'm concerned about damaging them during Vermont's winters. We regularly see a few weeks with highs below 0F and sometimes a night that gets as cold as -30F or so in the Champlain valley, and -40F in the rest of the state. To my knowledge, attempting to charge most lithium chemistries below 32F requires at best greatly reduced current. Charging too quickly (or at all, depending on the temperature) causes metalic lithium to electroplate the anode, which can result in the battery exploding or catching fire randomly. So, for 4+ months of the year I'd need either a battery heater, or to disable the alternator until the battery has warmed up.
I was reading about A123 Systems' LiFePO4 automotive batteries, and they rate their batteries down to (if I remember correctly, their site isn't loading right now) -30C, or ~-22F. If I were to speculate, they might have some combination of heating elements, BMS, insulation, or special chemistry that makes them able to accept charging at such low temperatures.
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