OK, there are two separate issues here:
(a) You have a LED. Therefore you need to drive it with a circuit to regulate current, be it a plain resistor, a linear current regulator or a switching current regulator (AKA LED driver).
Because of the high LED power a resistor is not a good choice. Linear regulators need the battery voltage to be always higher than the LED forward voltage and dissipate the extra power as heat. Switching regulators exist in various types (eg. boost, SEPIC and buck) and are more efficient.
(b) You want to decide on battery voltage so that circuit (a) is as simple, as cheap or as efficient as possible (add your own criteria here).
There are three possible design choices for the battery voltage \$V_\text{bat}\$:
- \$V_\text{bat}\$ is always below the LED forward voltage (\$V_\text{f} = 12\$V in your case). You need a boost converter.
- \$V_\text{bat}\$ is sometimes below, sometimes above \$V_\text{f}\$. You need a SEPIC converter or buck-boost converter.
- \$V_\text{bat}\$ is always above \$V_\text{f}\$. You can use a buck converter, or a linear regulator if \$V_\text{bat}\$ is close to \$V_\text{f}\$, but not too close (they need 1 to 2 V of extra voltage).
Now as for the current limit circuit, there are again three choices:
you can use a switching voltage regulator (boost, sepic or buck) to set \$V_\text{out} = V_\text{f} +\$ 1 to 2 V followed by a linear current regulator. But the losses of the two regulators will add up to 20-40%.
you can use a switching converter (boost, sepic or buck) that has a built-in output current limit. Because of this feature it's probably sold under the name of LED driver. Losses will be lower, 10-20%.
for the buck case only: calculate the power dissipated as heat in a linear regulator: \$P_\text{reg} = I_\text{LED} \times (V_\text{bat}^\text{max} - V_\text{f})\$ (using volts / amperes, not mA). If \$P_\text{reg}\$ is less than 1 to 2 W, you might be better off using a linear regulator only. That's because switching regulators have an efficiency of 80-90% and will waste 1 to 2 W anyways. If it's more than that, you should use a switching converter as described above.
You will find that buck LED drivers are easy to find. Boost and SEPIC LED drivers are harder to find and must sometimes be built from scratch. Buck and boost voltage regulators and linear current regulators are also easy to find.