On a typical day, my commute is only 30 miles both ways so I definitely don't need the whole range of the 21.5 pack.
Should I charge the bike up back to 100% SoC overnight? What is best for battery longevity?
If you need to stow away the bike for weeks, then lpr mode and < 80% is the way to go.
For daily riding there are two considerations:
1: Cell balance
2: Battery longevity.
For 1 you need to charge the bike slowly to full. It may take some days to get there-- (bikes that has idled or been fast charged much should always be charged full a few times to avoid having mandatory balancing while riding).
For 2, the "best" for battery is staying at around 50-60% charge+- - as defined by the cell chemistry (that may or may not be at 60% SOC, but likely close enough).
So since there are conflicting interests the real deal is how much does it count if you screw up one of them?
In case of 1, unbalanced cells may require your fast charge sessions to use hours for balancing- not a good way to spend your time when you need it. Also poor balance will leave you with less usable energy while riding.
In case of 2, well in the first 5-10 years, it is unlikely that you will see any difference at all, unless you actively search for it. Remember that 100% SOC is not 100% charge compared to what the battery chemistry allows (all manyfacturers reduce the maximum available charge, so that you shall experience longevity). Now There may be some differences- if you fast charge a lot or if you live in a very warm environment, storing the bike hot while charging.
If you mostly charge your bike indoor at 25 degrees Celcius or below (I do), there is very little chance that AC charging will break your battery, even if it is full every time.
If you DC fast charge a lot and most often charge and ride at the yellow status, your battery will wear out faster. Charging 80% or so rather than 100% may help, but you should then also make sure to go to 100% (using slow/ AC charging) about once a week to be on the safe side.
If your level of dedication is high, the probably best practice is charging to 80% during the week, and then once or twice to 100% during the week end. If you experience any balancing issue- charge to 100% all week.
For my own part, i charged my Zero to full always for 5 years, and i had no issues with cell balance (may be pure luck but who knows), and i wasnt able to feel any degredation although there probably was some. My EV-car (Ioniq EV) i always charge to full every night- it has passed 90kkm since 2017 and battery has never been an issue. I tried to see if charging to 80% was a viable route for me this autumn with the SS9+ i got this summer, but i think i have reached the conclusion (after 6kkm so far) that i will charge to 100% most of the time next summer, both because i want to keep balancing issues out of the way, and then i also tend to forget charging to 100% when i use the bike for leisure rides in the week end.
