There is no way I would buy an expensive one. They are way too easy to misplace. I got some of these disposable ones for second year, and they've worked great:

http://www.amazon.com/Primacare-DL-9224-Disposable-Diagnostic-Penlight/dp/B00CL6FDAS/ref=sr_1_sc_2?ie=UTF8&qid=1416496202&sr=8-2-spell&keywords=prima+care+pen+light

Granted, we are only seeing patients a half day/week--so I can't speak to the battery life, but when you are paying $6 for 6 of them you can't go wrong