What indicates that routine maintenance is needed on a battery?

Corrosion on the battery terminals is a clear indicator that routine maintenance is needed on a battery. This buildup often results from the chemical reactions occurring within the battery, especially when lead-acid batteries are involved. Corrosion indicates that the battery terminals may not have a good connection, which can lead to poor performance or starting issues. Maintenance in this case would typically involve cleaning the terminals, which can improve the battery’s efficiency and prolong its life.

Low charge, battery swelling, and frequent discharging can also suggest issues related to battery health or performance, but they do not specifically indicate the need for routine maintenance. A low charge may simply reflect the battery's current state of charge, and swelling usually signifies a more serious problem with the battery itself, such as overcharging or internal damage. Frequent discharging can indicate that the battery is not being used properly or is nearing the end of its useful life. However, these conditions do not directly lead to maintenance tasks as neatly as the presence of corrosion on the terminals does.