As others post, LED drop in flashlight "bulbs" have a number of advantages.
It is however well to be aware of a potential drawback, many of these bulbs are regulated, that is they give a near constant light output over a range of input voltages.
This means that the batteries are discharged to a much lower voltage before replacements are needed.

For example, 2 D cells driving an incandescent bulb would probably be replaced when the voltage drops to 2 volts/1 volt per cell.
With an LED bulb, a good light might be obtained down to 1 volt/0.5 volts per cell.
Batteries discharged that far are MUCH MORE LIABLE TO LEAK.
It is therefore most important to remove spent cells promptly.

If keeping nearly dead cells in order to "suck them dry" then I urge that these cells be stored in a box etc. and not in a flashlight. Put them in the flashlight when needed as then discard them promptly when the light dims noticeably.