A box arrived in the mail today with a dangerous (though legal) quantity of lithium-polymer batteries. These are manufactured for use in high-performance model cars, and as such have desirable characteristics for a DIY electric vehicle - high energy density, compact size, and high continuous output.
I briefly considered a battery pack made out of more conventional 18560 lithium-ion cells (the kind found in laptops and electric cars) spot welded together, but the batteries themselves are fairly expensive and building a spot welder is a bit beyond the scope of this project-- I'm saving this idea for the future though. My cheaper lithium-polymer packs do degrade faster and are far more unstable, but I've decided that this is worth it.
To determine what sorts of specs I'd need for the electrical system I did some calculations. LiPo batteries are marked with a capacity, voltage as an integer S-value, and max draw as a C-value. To convert to more sane measurements, actual voltage can be found by multiplying the S-value by the voltage per cell, and max current can be found by multiplying the C-value by the capacity.
I'm using four 5Ah 3s 25C batteries. I plan to wire these in two parallel sets, each containing two cells in series. This will make a 22.2V nominal pack with a capacity of 10Ah and a max draw of 250A -- more than plenty for me.
This is a diagram