Can I replace a NIMH rechargeable pack with a resistor if I only want to run plugged in?
In the spirit of fooling the battery charging circuit into thinking that it is attached to a charged battery and also getting at least a little light in the case of a power failure, you can replace the battery pack with an electrolytic capacitor instead of a resistor.

The charging circuit will charge the capacitor to the normal battery charging voltage and then the current will stop flowing.  This minimizes the heat generated by the charging circuit.  Just make sure to connect the capacitor with the same polarity as the battery.  For even more run time, you could use a supercapacitor.

The capacitor voltage rating must be larger than the battery charging voltage in order to avoid damage.  Note that the charging voltage is often higher than the rated voltage of the battery pack, so a 5V or higher rated capacitor should be used.

Standard electrolytics are about $1 and a small supercapacitor is only about $2, so I would go with the supercapacitor and the much longer run time.



(Picture of Illinois Capacitor DGH504Q5R5, which has a particularly good shape to fit in place of the battery pack)