Not sure if it's exactly pertinent, but If I remember correctly tesla recommends draining your battery to 20% then charging back up to 80% when driving on a road trip, but this if mostly for speed of charging. The car battery charges fastest in this half-full range, charging past 80% to 100% is a exponential rate like blowing air into an already full balloon, it gets harder as you reach 100%.. to their recommendation is not necessarily about battery health but more likely about reducing the speed of your mid-trip recharge.