strange beam characteristics

I just need some responses and thoughts on beam brightness. The situation involves two exact same pen style pointers, from the same company, both rated at 150 mw. The first pointer dims noticeably after multiple on/off activations and the beam brightness subsequently holds at that dim level during repeat activations. Upon reactivation, the dot appears very bright for approximately 1-3 seconds then dims down. The second unit does not dim at all and maintains a steady output, even after repeat activations. Both units were compared at room temperature (69 degrees F), and disposable alkaline batteries were utilized. I know this may be the simple outcome as a result of the nature of green lasers as previously explained elsewhere on the forum, such as warm up time etc., but if so, then why would one unit dim and the other remain at the same level of brightness? Thank you in advance for your help.

I forgot to mention. The dim beam appears less bright than a 75 mw pointer on a side by side comparison under the same conditions.