The service life of a forklift battery has always been accepted as being 5 years with discharge rates no more than 80% of the battery’s rated capacity with operating temperatures not exceeding 95F.
This correlates directly to the industry standard of forklift batteries being able to provide 1500 charge and discharge ‘cycles’ performed once over a 24hr. period. The discharge rate of 80% is calculated as occurring over the course of 6hrs; this being considered the number of ‘pedal-hours’ a forklift operator would use during a typical eight-hour work shift.
As an example, a 1000Ah battery discharged 80% should deliver 800A x 1500 cycles, or 1,200,000 amps over the course of its life. Battery maintenance (watering) would be required once per week depending on ambient operating temperatures and the actual depth of discharges. Monthly ‘equalize’ or ‘extended’ charges are also required to maintain cell continuity.
Conventional Charging describes the “charge-back” required to operate batteries as described above. One single discharge and one single charge in a 24hr. period, providing a 4-6hr. ‘rest or cool down’ period for the battery during the 24hr. schedule.
Typical charge-back times for Conventional charging are 8-12hrs dependent on the charger’s output. When comparing an 8-hour charge versus a 12-hour charge, the long-term effect on the life of the battery is negligible, especially so if the available ‘cool down’ period is over 4 hrs.
Most chargers are described as 100% or 80% versions, the 100% able to fully recharge a battery in 8hrs or less, and the 80% version in12hrs or less. Ideally, in a ‘heavy use’ operation where a battery is being discharged 80%, a 100% charger would provide more ‘rest or cool-down’ time beneficial to extending battery life. For moderate to light applications, an 80% charger provides ample charge-back capability.
Most all single-work-shift per day operations will realize a battery life of 5 years. Batteries of a higher quality can produce 60-70% of their rated capacity for 7 years or more and are significantly more resilient in higher demand and high temperature environments.
High quality batteries feature many design characteristics for additional life and performance; extensive plate protection, (wrapping),low-antimonial content grid composition, high-quality lead-oxide, and lower electrolyte density. Multiple design and manufacturing principles add further benefits that result in lower internal resistance, lower operating temperatures and extended battery life.
In many applications, one battery “cycle” per day isn’t enough battery power to complete an extended or two shift per day operation. A second battery is required and rotated to accommodate the additional power requirement.
The benefits of having a single battery capable of delivering adequate power for a two-shift operation are well known; no battery changing equipment requirements, reduced safety concerns, space saving and time are the most commonly referenced.
As vehicles are designed to accommodate height, width and other transport requirements, a larger or higher capacity battery cannot befitted in most forklift battery compartments. Opportunity Charging may provide users the ability to use one battery per vehicle. Generally, an operation requiring additional battery power requirements per 24hr period may benefit from Opportunity charging, opposed to rotating batteries.
Chargers described as ‘Opportunity’ have DC output values greater than conventional chargers and designed to deliver charge-backs in much less time. Typically, Opportunity chargers will re-charge an 80% discharged battery in 4-5hrs versus a conventional charge of 8-12hrs.
Users implementing Opportunity charging should be aware that their batteries will no longer deliver the 5 year or 1500 cycle life of batteries charged under a conventional charge back. Batteries used under an Opportunity charge regime will experience higher operating temperatures, increased electro-chemical activity (cycles) and increased maintenance requirements resulting in a shorter life span.
Although batteries using an Opportunity charge regime will not deliver the same “time-life” of 5 years, it is expected, that with good maintenance practices and a regimented charge-back schedule, quality batteries will still deliver near the same total energy potential.
For example, a 1000AH battery discharged 1000A over a 24hr period would provide an additional 200A of power during that period opposed to conventional use (800A or 80% discharged).
This would be a 20% increase in battery consumption per day. If a sufficient charge-back takes place at breaks, lunch, shift-changes or periodically throughout the work hours, the maximum 80% discharge rate will not be compromised. The battery is now delivering 120% of its traditional energy output in comparison to a conventional charge regime. Expectations should be that the battery’s “time-life” will be reduced, in the case of 20% battery use on a 1000AH battery, 1,200,000 amps will be delivered over a 48-month period.
Work-shifts vary considerably, and every application differs with respect to its battery power requirements. The same 1000AH battery delivering 1400A per day would result in the actual power usage of almost two batteries. This would result in the battery’s “time-life” being reduced to 2-3 years, most adversely effected by high ambient operating temperatures. As power requirements from a single battery increase, the charge-back DC output must increase to match the battery power requirement. The most effective systems will insure that batteries are not discharged beyond 60% during a 24hr. period resulting in greatest battery life.
Of greatest importance for all users implementing Opportunity Charging in their operations is to calculate accurately the
vehicles power requirements over the course of its operating schedule. This data provides the minimum charge-back (output) requirement of the charger to be selected as well an estimate of the battery lifespan to aid in effective budgeting and forecasting. Professionals will consider charge-back efficiencies, aging factors and operating temperatures. Most charger controls allow for fine-tuning outputs to aid in the best possible charge characteristics to extend battery life.
Battery maintenance (watering) is the single most important factor. Batteries must be maintained as closely to maximum water levels at all times. Batteries poorly maintained will experience highly elevated temperatures and much reduced life and overall energy capacity.
Charge-back intervals are critical. Failure to re-charge batteries on a specific schedule that result in discharge rates beyond 80% of rated battery capacity will reduce life extensively.
Battery monitoring utilizing data collecting devices that record usage rates and provide low-level electrolyte and high temperature alarms are critical to insuring optimum use patterns. Devices incorporating ‘temperature-compensation’ help protect batteries from heat damage during charge-back periods.
Key Features and Benefits
Thickest possible positive and negative grids; provide maximum efficiency through lower internal resistance factors, cooler-operating batteries resulting in longer life
Extra thick post and strap design provides maximum energy flow and lowest internal resistance factors, resulting in more efficient power transfer and lower operating temperatures
Full 5 layer wrapping of the positive plate; eliminates internal shorting, reduces internal resistance that resulting in lower maintenance intervals and longer life
Low-density electrolyte, (1285SG); reduces plate degradation and corrosion timeline, resulting in longer and better performance in high-heat applications with lower maintenance intervals
Additional battery modifications such as larger cable, intercell connectors and terminal connectors aid in reducing overall resistance resulting in better charging efficiencies