I am not sure if this is the best place to put this, but if I'm in the wrong place please tell me where I can go. So I know a peltier module is not the most efficient, however my goal is to make a hand warmer / cooler with a petlier module. My operating temperatures will be around 60f to 90f, nowhere near the max of most peltiers. My first question is can it be powered by a small battery? Second, would I need a heatsink with this kind of temperatures that I want to produce and if it's required, is there any passive cooling I can use without being thick? Third, is this idea practical?
For heating, it would be practical. There are battery powered coats that are currently on the market. A peltier module pumps heat, plus makes a heat; so you get more heat than electricity you put in. So instead of getting 100% heat from electricity in a resistive heater, you are getting 150% heat (for example) from electricity in a heat pump (peltier module in this case).
A heatsink will increase the efficiency by allowing more heat to be pumped. Lots of variables, but lets say an increase from 150% to 180%. Add a fan to that heatsink and say an increase from 180% to 200%. I would recommend starting with a heatsink at least, and increasing or decreasing the chosen voltage to achieve your desired temperature. If you have a 12v module, start with something around 6 volts. Remember not to drain lipo batteries too low and to watch battery chemistry or you could damage them or start a fire.