According to the information you provided, the label of the lithium battery for electric vehicles says 48V 60Ah, the maximum voltage is 58.6V, and it shows 53.9V after fully charged . This may be normal.
The full voltage of an electric vehicle battery will be affected by many factors such as battery type, capacity and condition. Generally speaking, the full battery voltage will be determined based on the battery's nominal voltage and battery capacity. For a 48V60Ah battery, the total voltage may be slightly higher than 58.6V, but it may also vary depending on the battery condition and charger performance.
Also, if you use it after it is fully charged or the battery voltage drops after leaving it for a while, this may be normal. Electric vehicle batteries will present a certain degree of self-discharge during use. Even if the battery is fully charged, the voltage will gradually decrease due to self-discharge.
If you think there is a problem with the battery you purchased, it is recommended to contact the seller or manufacturer for consultation and after-sales service.