Your batteries will last longer if you're only running one bank of lights. You would be powering 5 lights instead of 10. Each bank of lights is it's own separate circuit.
However, they are LED lights, so don't draw much juice anyway. I use 1.2 V, 1800 mAh, NiMH, rechargeable in mine and they will last me at least two months riding to work well before daylight, but I recharge them at the beginning of every month.