Lithium-Ion ebike batteries use a similar technology to your laptop or mobile phone. They can absorb about 500-800 charging cycles before the performance starts to degrade.
One full charge cycle is from 0% battery capacity to 100% battery capacity. If your battery is at 50% battery capacity and you charge to 100%, that only counts as 1/2 a charge cycle.
It is okay to charge the battery between rides, even if you only drained very little battery energy (you only rode the bike around the block).