Installation Manual

30
CYCLE LIFE
Battery manufacturers rate the cycle life of their batteries by comparing the level
of discharge on the battery and the frequency of cycling. Higher battery discharge
will result in shorter cycle life. In reverse, a smaller discharge percentage will
extend the expected cycle life of the battery as the battery will provide more
charge/discharges. To provide an example of cycle life, a 48V string of 8 x 6
volt S-550 models in series (428 AH capacity @ C20 ) which are consistently
discharged to 50% state of charge (214 AH of capacity drawn) and consistently
recharged to a full state of charge should provide approximately 1280 cycles
before end of life.
With traditional off-grid Renewable Energy systems, DOD is set to operate
between 20% and 50% to maximize the life of the batteries. Battery-based
systems are designed to allow a maximum 50% DOD as this offers a balance
between capacity vs. cycle life, also taking into consideration the cost
of replacement.
For grid-connected backup systems, Installers will typically design battery
banks to operate to a greater DOD percentage to lower initial installation costs.
Cycling with grid-connected systems is significantly less frequent than with
off-grid, where this may occur daily, a lower DOD is acceptable as long as the
customer understands that the overall cycle life is affected when they cycle
their battery bank beyond a 50% state of charge.