Is it normal for batteries or chargers to heat up while charging?

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

Although the surface temperature of batteries could reach 55°C 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.