Welcome to the Forum !
Ride in Peace - please understand in the eBike Space - handlebar control Displays only show "approximated battery level" based on battery voltage
"Missing 1 battery bar after full charge" is not necessarily a defect or misconnection - "most" would consider "normal".
If you have LED battery level indicators on the battery case - again same thing "shows approximated" battery level as well.
For those owners into "voltage/battery level" a separate Digital Voltage Display connected directly to the battery cradle is the "most accurate reading".
So you know for BEST Battery Life - (1) After a ride - wait 1hr-2hrs after a ride to let the inside battery cells to cool down- charge only after coold won to reduce heat degradation of your eBike battery (2) try to normally Charge Up To 80% -unless you need a full 100% charge for your next ride (3) Always disconnect charger from your bike after you complete your charge cycle (4) for Winter store your battery (with or without bike) inside (5) while your battery or bike is stored - max charge for storage is that 80% - regularly check your battery every 2-3 weeks and recharge when it hits 20%-25% charge back up to 80%