What are the reasons why a maintenance-free car battery cannot be charged?

[FaithDella]

Reasons why a car battery cannot be charged: 1. The charger's converter is damaged and cannot convert or charge, requiring replacement of the charger resistor; 2. Or the charger fuse is blown, necessitating replacement of the charger; 3. The power cord is detached or has poor contact at the battery socket, requiring inspection and replacement. The batteries used in cars are lead-acid batteries, and the main reason for failure to charge is sulfation of the plates. For batteries that have been used for a long time, there is basically no value in repair, and they should be directly replaced with new ones; for batteries that have been used for a short time, if the plates are mildly sulfated due to short-term excessive discharge, they can be repaired using a desulfation charging method, but the battery capacity can only be restored to about 80% of its rated capacity.

[DiMila]

I've encountered this situation too. Maintenance-free batteries not charging is quite common. Severe sulfation due to battery aging or dried-up electrolyte makes it impossible to store electricity. Or if the car isn't used for a long time, the battery discharges deeply and gets permanently locked when voltage drops below 12V. Using the wrong charger can also cause problems, like when a regular charger doesn't match AGM battery characteristics and damages the internal plates. I suggest first testing the voltage with a multimeter - if it's below 10V, it's basically beyond saving and needs replacement. Generator failure could also be the culprit, like poor charging circuit contact or worn generator brushes preventing charging. Driving regularly for at least half an hour can delay sulfation - never let it completely discharge and die.

[CassandraAnn]

My friend's new car just passed three years, and the original maintenance-free battery can't hold a charge anymore. I've figured out a few key points about this situation: Low temperatures affect performance, as the battery's activity decreases in sub-zero conditions, leading to a sharp drop in charging efficiency. Corrosion or oxidation at the charging port causes poor contact, making it seem connected but actually preventing current flow. Forgetting to turn off the headlights or the dashcam while the car is parked drains the battery, resulting in over-discharge. Using inappropriate charging equipment, such as fast chargers with high currents, can physically damage the battery plates due to impact. For prevention, it's best to start the engine once a month to let the alternator recharge the battery, which can extend its lifespan by at least half a year.

[StCayden]

The core issue of a maintenance-free battery not holding a charge lies in increased internal resistance or internal short circuits. Damage to the battery's internal separators or deformation of the plates can cause direct current leakage. Manufacturing defects, such as seal failure or electrolyte leakage, are irreparable. Frequent short-distance driving, where the alternator doesn't have enough time to fully charge the battery, also accelerates aging. For diagnosis, first test with a charger; if it displays an error code, the battery is beyond recovery. It's recommended to use a smart charger that can automatically identify the battery's condition and attempt recovery. Avoid forcing a charge on an old battery with a regular charger.