Measure the voltage at the battery terminals with an accurate voltmeter. If the measured value is less than 10 V, the charging current will be very low and additional charging time will be required.
Place the charger in a high place. Some chargers have a reverse polarity protection circuit that prevents charging if the battery terminals are not properly connected. A fully discharged battery does not have enough voltage to power this circuit, even if the wires are connected correctly. This will result in the battery not being charged. Therefore, follow the charger manufacturer's specific instructions for the charger to turn on and start charging the battery at low voltage.
The chargers have voltage and current regulators. The times required to charge the battery depending on the different voltages are shown below.
Battery charging time depending on the initial battery voltage
If the charge received by the battery cannot be measured after the charging time has elapsed, the battery should be replaced.
If the received charge is measured during charging, then the battery is good and charging should be completed in the usual way.