It depends a bit on the driver circuit , you can put as much as 38v into an LM317 circuit without raising the output, (the excess voltage gets turned into heat). I am using a rkcstr with 3 10440 3.6v batteries, driving an 803T LD with no problems.
Most drivers we use are constant current, so as long as you keep the voltage between the upper and lower limits for the regulator you should be OK.