Whether it’s battery lamps (or batteries). Solar, shake or dynamo lights are just useless gadgets, often of the worst possible quality. Lamps with crenelated heads are expensive and give you no tactical advantage.
What do you have to look for?
The critical points to consider for an EDC lamp are from my point of view, the power and the modes of illumination, the autonomy, the type of batteries used, the resistance to shocks, the sealing and the user interface. The question of the type of bulb does not arise today: the LED is queen. Read some tactical flashlight reviews to get more info on these.
Regarding the power, I already spoke on the subject. Just remember that 20 to 30 lumens are enough for most tasks, and staying power is just as important as maximum power. Promote low power modes very low (1 to 5 lumens) that will illuminate for a long time without going dead.
Regarding the autonomy, opt for regulated models, whose voltage is kept constant by an electronic circuit. In the absence of regulation, the light intensity gradually decreases as the batteries are discharged which is not ideal. With regulation, the light intensity remains almost constant until it drops rapidly when the batteries are empty.
As for the types of batteries, the subject had also already been discussed across the internet. My preference is for common batteries (mainly AA). AA batteries are easy to find and cost-effective. AAA batteries have the advantage of their compactness at the expense of power and less autonomy. To use if compactness is really important.
The question of the interface is very personal. For my part, I hardly understand to use a lamp that would be devoid of a tactical button on the back. This is the way to activate the lamp that I find the most natural every day, and the most usable in a defense context when the lamp is used as a baton.