Charging a Very Flat or Completely Discharged Battery

The following procedure should be used to recharge a very flat or completely discharged battery.

1. Measure voltage at battery terminals with an accurate voltmeter. If below 10 volts, then charge current will be very low and it could take some time before it accepts a current in excess of a few milliamperes. Such low current may not be detectable on ammeters available in the field.
2. Set battery charger on high setting.
3. Some chargers feature polarity protection circuitry which prevents charging unless charger leads are connected to battery terminals correctly. A completely discharged battery may not have enough voltage to activate this circuitry, even though leads are connected properly, making it appear that battery will not accept charging current. Therefore, follow the specific charger manufacturer's instruction telling how to bypass or override circuitry so that charger will turn on and charge low-voltage battery.
4. Battery chargers vary in the amount of voltage and current they provide. Time required for battery to accept measurable charger current at various voltages may be as follows.
   • Charge current is still not measurable at the end of charging time.
     • Replace the battery.
   • Charge current is measurable during charging time.
     • Battery is considered to be good and charging should be completed in normal manner.

   Battery charging time 

   16.0 V or more: Up to 4 hours 

   14.0 - 15.9 V: Up to 8 hours 

   13.9 V or less: Up to 16 hours 

5. It is important to remember that a completely discharged battery must be recharged for a sufficient number of ampere hours (AH) to restore it to a usable state.

   As a general rule of thumb, use nominal AH plus extra about 30% as number of ampere-hour of charge, which will usually bring green dot into view.

   If battery is 45 AH, required AH for complete recharge will be 45 x 1.3 = 58.5.

   Therefore, following low ampere long hour charge will be recommended.

   • 3 ampere charge x 20 hours... 60 AH or
   • 5 ampere charge x 12 hours... 60 AH, etc.
6. It is recommended that any battery recharged by this procedure should be Load tested to verify serviceability.