Viewing Forklift Battery Charging from a Total Lifecycle Perspective
All rechargeable forklift batteries have a finite lifespan, one that is consumed both when the battery is in use and when it’s being charged. In fact, the length of a battery’s effective life is often more dependent on how it’s charged than how it’s used. For example, poor forklift battery charging practices can lead to higher lift operating costs, lower utilization rates, and more frequent battery replacement. With this in mind, let’s explore the most common types of industrial forklift batteries and how warehouse managers can extend their lifespans by making a few simple decisions about how they’re charged.
To begin, let’s define the two primary types of electric forklift batteries used in industrial material handling applications:
- Lead Acid Batteries – lead acid batteries are viewed as the “traditional” battery design, drawing their roots back to the 1800s. This design utilizes lead oxide and lead plates submerged in a liquid mix of sulfuric acid and electrolytic water to generate electricity. These batteries are large, heavy, slow to charge, and require ongoing maintenance, but are also lower in cost, mature in technology, and widely adopted.
- Lithium-Ion Batteries – lithium-ion batteries are the newer and more advanced option of the two battery types. This battery design uses aluminum, lithium oxide, copper, and graphite materials suspended in anhydrous electrolytic liquid to generate electricity. Lithium-ion batteries require less maintenance, and charge much faster than lead acid batteries, making them more efficient though at a higher cost.
For simplicity, we’ll limit our discussion to these two most common battery types, but it is worth noting that there are other battery designs (for example, absorbed glass mat) as well as multiple variations of each of the above designs (for example, gel cell lead acid) plus other forklift power options available on the market.
Optimal Charging Frequencies for Forklift Battery Types
When thinking about forklift batteries in terms of their total lifecycles, we suggest breaking things into five distinct factors:
- Charging Frequency – this value is the common period of time between battery charges. As a baseline, conventionally charged lead acid batteries are commonly charged for up to 8 hours, cooled for 8 hours, and then used for 8 hours, equating to a 16-hour charge frequency. With opportunity charging, however, lead acid batteries are charged more frequently throughout the day, for 15-30 minutes during each lunch or break time. Lithium-ion batteries charge much faster and do not need to be cooled afterwards, so can be charged on an 8-hour frequency across common warehouse shifts.
- Charging Duration – charging duration describes how long it takes to charge a battery. This value changes based on the use-case and the type of charger being used. Lead acid batteries typically take up to 8 hours to charge, whereas lithium-ion batteries typically take 1-2 hours to charge. Advanced charger technologies can improve these times, which we’ll cover more later in the article.
- Total Charge Cycles – each battery type has a finite number of charges that it can take before it is considered depleted. Lead-acid batteries commonly provide up to 1,800 charge cycles, and lithium-ion batteries up to 5,000 charge cycles.
- State-of-Charge Level at Recharge – each time the battery delivers 80-100% of its rated capacity, it is considered one charge cycle. That’s why managing charge cycles is paramount in maximizing a battery’s life. Ideally, lead acid batteries would be depleted to 20%-40% before recharging, and lithium-ion batteries below 50%.
- Total Year Lifespan – when we look at the above four factors, we can extrapolate the battery’s total lifespan in years is based on how often the battery is recharged. Businesses that rarely utilize their lifts will recharge less often and experience longer battery lifespans, whereas businesses that recharge daily will experience shorter battery lifespans. Generally speaking, lead acid batteries are estimated to last 3-6 years and lithium-ion batteries are estimated to last 5-10 years. It’s important to note that heat, throughput, and general maintenance practices will also influence those lifespan estimations.
To summarize the average lifespan that can be estimated based on the battery type and charging frequency which we’ve discussed above, here’s a concise table:
| Battery Type | Charging Frequency | Charging Duration | Total Charging Cycles | State of Charge Level at Recharge | Total Year Lifespan |
|---|---|---|---|---|---|
| Lead Acid Batteries | Once per day (Conventional Charging) | Up to 8 Hours | 1,500 – 1,800 | 20% – 40% | 5 – 6 years |
| Lead Acid Batteries | Multiple times per day (Opportunity Charging) | 15 – 30 Minutes | 1,500 – 1,800 | 20% – 40% | 3 – 5 years |
| Lithium-Ion Batteries | Every 8 Hours | 1 – 2 Hours | 3,000 – 5,000 | 50% | 5 – 10 years |
How Charging Technologies Relate to Charging Frequencies
From the above, readers can now see that a forklift battery’s lifespan is entirely dependent on how often and how completely it’s recharged. This tells us that to maximize a battery’s life, it needs to be charged as infrequently and from as low a depletion level as possible. Unfortunately, this goal doesn’t align with most industrial warehouse demands that push for maximum forklift uptime. In fact, multiple advanced charging technologies are available today that can charge batteries in shorter bursts and at faster rates just to achieve this uptime, albeit at the expense of total battery life.
- Conventional Charging Systems – these systems are designed to charge batteries from near depleted to fully charged in a single, long charge cycle. These charges match the “charge duration” times mentioned above (8 hours for lead acid, 1-2 hours for lithium-ion). In general, these chargers support the longest lifespans for batteries at the lowest utilization levels. (Note: to keep things simple, we are making this statement considering on-lift charging, not swappable battery charging).
- Opportunity Charging Systems – these systems are designed to charge batteries from low charge to near-full charge, intentionally stopping short of full charge. These systems fulfill an operational schedule objective of partially refilling batteries during windows of opportunity in an operator’s schedule such as during lunch or breaks. These chargers are typically slow and use variable voltage profiles so as to reduce heat and avoid damage. Opportunity charging is highly unadvised for lead acid batteries as the slight benefits of extended runtimes hardly justify the lost lifespan and potential for damage. Instead, opportunity charging is best for lithium-ion batteries, as “topping off” these batteries intermittently throughout the day increases uptime without noticeable loss to lifespan.
- Fast-Charging Systems – also known as rapid chargers, fast-charging systems are advanced, intelligent technologies that can charge lithium-ion batteries in the shortest amount of time possible. Rapid chargers achieve this by using logic-based charging profiles that push higher voltages into batteries while directly measuring and mitigating temperature, chemistry, physical damage, and overcharging risks. Rapid charging is a unique benefit of compatible lithium-ion batteries (which must be specified as fast-charge compatible) and is not available for lead acid batteries. Such lithium-ion batteries can reach the highest levels of utilization without prematurely eroding their lifespans.
While these options all speak to charging batteries faster, let’s return to the fact that total lifespan is a function of how frequently batteries are charged. As we can see, using opportunity and rapid charging solutions allows us to fit in more charges into the same time period, but will also consume the battery’s available charge count sooner than using conventional charging.
So, here lies the operational balancing act: to maximize battery lifespan while also achieving productivity goals, fleet managers should employ a combination of the above charging methods across their fleet. Ideally, opportunity and fast-charge methods should be used when maximum uptime is absolutely required, but for the rest of the time, batteries should be run to lower levels and charged in less frequent, longer cycles. In this way, battery lifespans can be drawn out as long as possible simply by managing how frequently they’re charged.
We hope that this discussion has been helpful for your commercial material handling needs. Fairchild Equipment is the Upper Midwest’s premier Material Handling Equipment and Forklift Service resource, with headquarters in Green Bay, Wisconsin, and numerous locations in five states ready 24/7 to serve your needs. For more information or to discuss which forklift power solution might be best for you, please send us a message or give us a call at (844) 432-4724.
