Minimum AWG of a battery wire
Maximum AWG depends on the current, which you did not specify. There is no minimum AWG, but it would be a bit silly to use 0000 (4/0) wire for a small battery.

It also good to have a wire that is physically robust, so AWG 20 to 24, maybe 28 are reasonable. The maximum ampacity also should not be exceeded. 

Assuming 50mm (100mm round trip), then you wish the maximum voltage drop to be 0.02*3.7 = 74mV. Referring to a wire table we can determine the maximum current for each wire gauge. Resistance for 0.1m is 3.3/5.3/8.4m\$\Omega\$ for AWG 20/22/24 wire. Refer to this table for ampacity,

So the maximum current would be limited by wire ampacity, and you should just select a wire that is physically robust unless your current is very high.