A charger with an output voltage of 60 volts cannot charge a 60-volt battery. It must be charged with a charger higher than 70 volts.

In general, if each battery is 12 volts, the reading obtained by connecting five batteries in series with enough meters is close to 70 volts, which is electromotive force rather than voltage. When the battery outputs a certain current (such as wheel rotation), the reading at both ends is voltage, generally 60 volts.