Resistors are a pretty ugly way to do it IMO.

Some like this:
https://www.ebay.com.au/itm/AC-100-240V-...m-/221399192313

But yeah 5V supplies are common. The 3xAA unit would likely run just fine directly off 5V (think 3 x 1.66V batteries)

Or something like this if you can solder - guessing probably nto given the question smile
http://www.ebay.com.au/itm/DC-DC-Step-Down-Buck-Mini-Module-3-3v-5v-6v-9v-12v-Adjustable-Voltage-Regulator/112426265937?hash=item1a2d20ad51:g:fVwAAOSwH3NXmsyx
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Christian
#40104192 120Gb (no longer in my E36 M3, won't fit the E46 M3)