The hazard is proportional to the charge/discharge curve differences which are related to the voltages.
You can disregard discharge differences since it simply means some batteries will draw more current than others. Ignoring charge differences could result in overheating if there was overcharging. If the charging circuit shuts off at the nominal voltage then the hazard is limited to those batteries that WILL NOT charge to that voltage. What does all this mean ? It means you need to check all the batteries one by one and write their voltage on a label you stick on the battery. Remove and discard any that are out of tolerance.