What are the reasons why the battery still doesn't show fully charged after 12 hours of charging?
2 Answers
Battery full charge indication is generally based on the light turning green. However, this isn't always accurate in reality. Overcharging should be avoided, and the charging time should not exceed 10 hours in principle. The most accurate way to measure whether a battery is fully charged is by the charging capacity, which is generally 1.03~1.05 times the discharge capacity. There are five main reasons why the light doesn't turn green: 1. Current too low: The charging time is prolonged, preventing the battery from being effectively fully charged within the expected time, causing the charger not to switch the light. 2. Ambient temperature too high: The charging voltage at the battery terminal fails to reach the limit voltage value, keeping the charging current at a relatively high level without dropping to the inflection point current value, thus preventing the charger from switching the light. 3. Parameter mismatch: The charger's parameter settings don't match the battery, leading to long-term overcharging or undercharging of the battery, eventually causing water loss in the battery and preventing the charger from switching the light. 4. Abnormal acid volume: Excessive internal acid volume in the battery hinders the oxygen cycle inside the battery, causing "thermal runaway"; insufficient acid volume, combined with water loss in the later stages of battery use, both prevent the charger from switching the light. 5. Internal micro-short circuit: A micro-short circuit inside the battery prevents the charging voltage at the battery terminal from reaching the limit voltage value, keeping the charging current at a relatively high level without dropping to the inflection point current value, thus preventing the charger from switching the light.
I've encountered this situation before too. That time, the battery took forever to charge but just wouldn't reach full capacity, which was really frustrating. The main reasons could be charger malfunction - perhaps its internal circuitry is damaged or the power output is too weak to deliver sufficient current. Another possibility is that the battery itself has aged. Like the five-year-old lead-acid battery in my old car - once its capacity degraded, no amount of charging could fill it up. Also, don't overlook connection issues. If the charging clamps aren't secured properly or the contacts are rusty, poor contact will prevent power from entering. I later discovered it was loose clamps in my case - tightening them solved the problem. If all these are ruled out, consider low ambient temperature - batteries charge slower in winter, so try doing it in a garage. Remember not to force charge, as overheating could be dangerous. It's safest to have a professional shop check the voltage - safety first.
