they can leak if you crack their casing. i know that sounds obvious, but in many cases we speak of putting these things all over the place. they have a thin plastic outer shell that can crack. that red top is the top of the battery not simply a red fascia. if you hit them hard enough or cruch them, they will break open. the one i originally ordered from OK4wd can from them with a crack in the red fascia, which i thought was nothing. i didn't install it immeditaly cause i was waiting to install my winch. 2 months or so after getting it installed and all, it would not keep a charge. i opened the hood there was a HUGE hole in the battery where the crack was when I origianally got it. my guess is that UPS dropped it and it cracked.
so don't anyone think that these things are indestrucbilble.