[EricH]

Originally Posted by the man

There is a type of lithium battery something with iron phosphate maybe. [...] The lithium batteries have a more favorable voltage cure, they are lighter, plus they last considerably longer cycle wise, enough to make up for the cost. I am in favor of them except that special chargers and battery management systems are required to use them.

The LiFePO4 type batteries are pretty expensive.

Here's a cost comparison from my senior design project, LiFePO4 compared to sealed lead-acid (SLA). Note that in this particular application, weight is a HUGE disadvantage, to the tune of -10 points per kilogram (and any GDC members reading this: don't get any ideas, please!). I want to say that it's a total of 24V available, but for competition we're running 12V.

Cost (for 2 12V cells)
SLA: $72
LiFePO4: $358 (plus $50 for charger)

Weight (for 2 12V cells)
SLA: 12.7kg
LiFePO4: 6.5kg