Converting an LED bike light to use Ni-Mh's instead of Alkalines and SMT resistors

I've got a couple of bike lights that runn of 4xAAA batteries, and when I use Ni-Mh's, the lights are bright, but not as bright as wiith alkalines.

I dismantled one of them last night, and found 5x5mm LEDs in there, and 5 6 ohm resistors.

With a bit of maths and some assumtions, I reackon the LED's must get 3v from alkalines, and only 1.8v when being driven by NiMh's.

Maths (for those that are interested):

Led's are assumed to use 20ma. 5 x 20 ma = 100ma combined current. 100ma = 0.1A

Now to work out the voltage drop of the resistors. There are five resistors, so 5 x 6ohm = 30ohm

V = IR = 0.1A x 30ohm = 3v

so the voltage drop is 3v.

Now with a bit more maths, I reackon if I substituted the 6 ohm resistors for 3 ohm ones, I would get half the voltage drop... 1.5v

I'm assuming my NiMh's will give out 1.2v so 4x1.2v = 4.8v

4.8v = 1.5v = 3.3v to the leds. Perfect. Apart from the fact that I've had problems finding 3 ohm resistors, so it looks like I'm gonna have to settle for some 3.3ohm ones.

3.3 x 5 16.5

V = IR = 0.1 x 16.5 = 1.65v which is still ok tho. 4.8v - 1.65v = 3.15v.

Now... I'm pretty sure I've got the theory ok. I'm a bit stuck when I came to order the resistors... I've only ever used the barrel type with wires coming out of each end. After looking at my bike light, it has some funky surface mount resistors. They are a few mm long an probably less than 1mm wide. I could prpbably solder it, but I'm not sure what package type to order. Does anyone know what I should order, or maybe just some info on surface mount stuff. Also, let me know if any of my maths is wrong, let me know as I don't have any spare 5mm white leds handy.

Re: Converting an LED bike light to use Ni-Mh's instead of Alkalines and SMT resistors

Regarding your maths - not wrong per se, but probably based on a false assumption:
If you have 5 LEDs and 5 Resistors, it's likely that each LED is fed by its own resistor, or even that the resistors are wired in parallel (lazy option, although bad for the LEDs). Just keep in mind that a white LED needs at least something like 3.4 Volts to operate (going down to maybe 3 Volts if you want it to be about glowworm-bright).
Regarding your resistors: can't help you there without better numbers. SMD resistors come in a variety of sizes, the number code denoting the (geometrical) size of the package. 1210 is already quite large, and since you say it's less than a millimeter across, it's likely to be an 0603, 0402 or 0201 package. For manual soldering, I'd use 0805 size and stick them on with sufficient solder - the nice thing about SMD resistors is that you can just solder one on top of another if you want to reduce resistance by paralleling the resistors.

Bye
Markus