If you keep the charge between 20 - 80%, your battery will last for far more cycles than when charging 0 - 100%. So you'll only get 60% of the kWh per cycle, but the battery will do 3-6 times as many cycles.

In fact, the battery management system won't even let you fully charge or discharge the battery for exactly this reason. When it shows 100%, there will still be 1-2 kWh empty and the same for a zero percent charge.

For example, a Toyota Yaris use a tiny (0.7 kWh) lithium ion battery and it gets charged/discharged constantly while breaking/accelerating, but it still last a long time because the charge is kept at about 50%.