I think it's important to note that it's hard to get a deep discharge (0%) with most devices (including our phones) because when they get low they turn off.

I wouldnt worry too much about draining them completely; but I would worry about letting them sit in hot conditions for long periods of time (i.e. in the car under the sun or attached to a charger that is functioning incorrectly and causes it to overheat)

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MCSE: Messaging 2003; Windows Server MVP