What Magic says is all true, additionally we are finding that there is a fairly wide range of "normal" power consumption from the different types of locaters. Some or most of that has to do with factory or user programming. When you start using the more sophisticated locaters you will find that there is less voltage tolerance and greater power consumption if you want to take advantage of all the features provided by those devices.
Even on the most basic types of locaters these things affect power consumption:

Backlight, the #1 cause of battery drain (not counting leaving it turned on all night - I wish locaters would have an auto off feature). I would not use a locater that cannot have the backlight programmed to be off at all times, except when fishing at night of course.

Display screen type: Color and especially HD screens use more power. Black/white grayscale, though a bit trickier to interpret, use less.

Deep water use also requires more power. I'm not suggesting to never use it over deep water, just something to keep in mind if you're trying to conserve.

Alarms, turn them all off to save power. Nobody else really wants to hear them anyway.