I have a way to measure battery power

[TravisE]

If it's like most other consumer Li-Ion battery systems, staying plugged in to the charger shouldn't cause significant damage because it's smart enough not to continue to charge when it's not necessary. Leaving the battery near drained for extended periods of time might not be a good idea; I've heard Li-Ion batteries can be destroyed if allowed to self-discharge too far. Deep discharge/charge cycles shouldn't be necessary; they should be just fine with partial cycles (they'll normally last more cycles this way, in fact). The only real reason to purposely do a deep discharge cycle might be to recalibrate the battery gauge occasionally, but this isn't always necessary.

I've noticed that my Prime seems to refuse to charge at all (at least according to the display) unless the battery has dropped at least one bar of charge from “full”. Many devices will try to gently top off the battery even if already fairly close to a full charge; perhaps this more conservative behavior was implemented as a way to help improve the battery lifespan.