With Maglites, batteries that leak and get seized in there are almost impossible to get out without damaging the light. I switched to 9.6 volt Makita flashlights, or old fashioned lights using carbon-zinc batteries. (Don't know if they make those anymore).
For new flashlights, I fashion a sleeve out of an old toilet paper tube (or paper towel tube for longer batteries) as a buffer between the light and batteries. Any liquid that does leak out gets absorbed by the cardboard, saving your light if not left too long.