Is it normal for batteries or chargers to heat up during the charging process?

Heat generation during charging is not abnormal. However, how much a charger heats up depends on:

• The type of charger that is being used (quick charging versus normal charging)
• Whether or not a protection cover is being used
• The initial capacity of a rechargeable battery
• The remaining capacity of a rechargeable battery
• The degree of degeneration of the battery
• Ohers

Although the surface temperature of batteries could reach 55 degrees Celsius while being charged, this will pose no problem. Chargers are fitted with functions to stop the charging or control the temperature of the batteries as soon as a possible risk is detected.