Should I drain my battery on my Nexus before charging it again?
No. With the newer batteries, it's bad for them to be completely drained before charging. If possible, avoid completely draining the battery.
Maximum life for lithium batteries is at 70% charge and in the refrigerator. The capacity decreases with every charge cycle so the more you discharge and charge it, the faster it will lose total capacity. With a properly designed charger it seems you would always be better off using the charger to reduce the discharge/charge cycles. The additional loss due to being at 100% charge is probably not an issue.
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