I’d start with a 10 Ohm resistor in series, probably with a 2 Watt rating. This may get you down to the 200mA range. Not sure how bright you want it. Higher value resistors will give lower current, lower will be higher current. 4.7 Ohm may also work, it really depends on the Vf of the LEDs in the strip.
If you build a timer circuit to PWM this, you will also need a FET to do the switching. There should be circuit examples on the web. Set the frequency to at least 4kHz so the PWM isn’t visible.
Good luck!
If you reduce steady-state current by 50% with a resistor, you’ll still get ~60% of the Luminous output.
If you reduce duty cycle to 50, you’ll get ~50 of the Luminous output.
The eye responds to something in between so PWM may give you more bang for the buck.
In cold weather your battery may be seeing up 15.5v. Also there is a ‘load dump transient’ in vehicle electrical systems so you may want to put some diodes, zeners, resistors and capacitors to filter this out. National Semiconductor App Notes had a simple circuit for this to use with their automotive/special function ICs.
Read the pdf & note how various mw from a single led is done.
BTW, 880nm is invisible to the naked eye, this is night vision illumination long-range.
Re: my strips, they are white, I’m hoping to cool them w/short duty cycle.