Technical Manual

Document No. 6-0101 Rev. F Page 20 of 40
The following table provides recommended absorption times for Lifeline® Batteries:
Table 5-2 Recommended Absorption Times
Average Depth of Discharge (DOD)
Absorption Time
Less than 30%
2 hours
30 – 50%
3 hours
More than 50%
4 hours
The absorption time may need to be fine-tuned from these values to assure the batteries
consistently reach full charge per the criteria given above (charging current is less than 0.5% of
battery’s rated capacity).
The charging current during the Bulk stage should be set as high as practical; higher current
levels mean faster recharge time and less time for the plates to become sulfated. Due to the
low impedance design, Lifeline® batteries can tolerate in-rush current levels as high as 5C
(500A for a 100Ah battery). The time to reach full charge at temperatures in the range of 20-
30°C (68 to 86°F) can be estimated from the following equation:
Charge Time = [(DOD/100) x Rated Capacity (Ah) ÷ Output of Charger (Amps)] + Absorb Time.
For example, charging a 100Ah battery at 40% DOD with a 25A charger would take:
[(40/100) x 100 ÷ 25] + 3 = 4.6 hours to reach full charge.
If a 10A charger is used, it would take:
[(40/100) x 100 ÷ 10] + 3 = 7 hours to reach full charge.
Note that this formula is approximate and the full charge state should be verified using the
criteria given above (current drops below 0.5% of rated capacity). If the recharge does not
return 102 to 110% of the discharged capacity, the battery’s state of charge will gradually “walk
down” as it is cycled leading to premature failure. Therefore, it is important to verify that the
battery is not being undercharged.
For repetitive deep cycling applications (deeper than 50% DOD), chargers should have an
output current of at least 0.2C (20 Amps for a 100 Ah battery). If the output current is less than
this value, the cycle life of the battery may be negatively affected. If a charger with at least 0.2C
output is not practical, an alternative charge profile using a low rate constant current stage at
the end of the absorption stage will normally improve the cycle life. The constant current stage
should be at 0.02C (2 Amps for a 100Ah battery) for no more than one hour.
Some types of battery chargers allow the user to input the Peukert constant to obtain an
optimum charging profile. For Lifeline® batteries, the recommended value of the Peukert
constant is n = 1.12.