Does proximity matter when hooking up batteries?
Every piece of wire you add in a circuit, acts like a resistor. Ohm's Law kicks in when that wire is carrying any non-trivial amount of current, causing voltage droop. You're adding a few ohms of resistance. You can minimize and measure it by taking the wire size (in AWG), and looking up the resistance for the length of your cable (Plenty of handy calculators online like this one).

For example, adding 2 feet of 20 AWG wire, which has 10.15Ω per 1000 ft, would only add 0.0203Ω of resistance. Your  At low voltage and/or current, that's fairly negligible, so you shouldn't have any problems. Consider a AA battery might have a Internal Resistance of 0.1Ω! Physically bigger wire has a lower resistance.