For battery use I would use a two-transistor constant current driver,
so you have the same performance when battery voltage drops.
The drive transistor can be a mosfet or 2N2222/BC337. Feedback could be BC547.
Calculate Rsense for 0.65volt drop at the required peak current.
3.3 ohm could be a good value (~200mA peak).Rbase could be 330 Ohm.
Leo..