Charge Specific Gravity (Sg) 12v 6v FreezeCharging Time
100% 1.265 - 1.285 12.6 - 12.68 6.3 -71°F
75% 1.220 - 1.225 12.4 - 12.45 6.2 -33°F
50% 1.175 - 1.190 12.2 - 12.24 6.1 -15°F
25% 1.140 - 1.155 12.0 - 12.06 6.0 + 4°F
Dead 1.110 - 1.120 11.8
1. Down and Dirty Charge Rate Method - Chargers with Ammeters
Charge the battery until the charge rate (as indicated by the charger ammeter) has dropped and stabilized at 1/3 to 1/2 of the charger's full output rating. For example, a 10 amp charger will stabilize at 3 to 5 amps. This is an inaccurate method and care must be taken not to overcharge.
2. Down and Dirty Bubble Method
When the battery fluid is gently bubbling, the battery should be considered charged. This is a very inaccurate measure of charge state and care must be taken not to overcharge.
3. Voltage Method
Charge the battery until an accurate digital voltmeter indicates the following end of charge voltage:
Temperature Conventional Maintenance Free
95°F 14.2 volts 14.5 volts
75°F 14.4 volts 14.7 volts
0°F 15.1 volts 15.4 volts
4. Specific Gravity Method - Not for Maintenance Free Batteries
Charge the battery until reaching the 100% charge specific gravity (Sg) shown in the Charge State table above. Disconnect the charger before testing. Older batteries or batteries with sulfated plates will reach full charge at a lower Sg; continued charging may result in damage.
5. Calculation Method
Determine the percent of charge needed (use either a hydrometer or voltmeter, and refer to the Charge State table above). An approximate charge time in hours, "Time", can be calculated as follows:
Time = .667 (RC) (Charge Needed)
Time = 1.6 (AH) (Charge Needed)