I have bunch of 18650 batteries that are reading below 1.6V. I tried charging one and the charger seems to charge it at 500ma. Should I continue or am I just wasting my time because it won't hold the charge? I head that below 2.8V batteries are considered dead.
Below 2.8V Standard 18650 cells are considered "dead" in the sense that they are empty. "Dingles! My battery is dead, gotta go charge that thing."
Below 2.5V one of those batteries is considered "at risk", which is that it may get damaged.
Below 2.0V that becomes quite a bit more likely.
So if your batteries have been at 1.6V, they have a better than decent chance of being damaged. It's not an absolute guarantee, but the chances are good enough to say:
Stop charging them!
Not because there isn't a chance you can get some energy in. Quite the opposite, because there's a chance that you might get enough energy into a damaged one that you risk severe injury (and/or FIRE!!1!) if it ends up creating an internal short.