A User’s Guide to Forklift Battery Types

Searching for a forklift power solution? As technology advances and options proliferate, you may feel overwhelmed by choice. From traditional lead acid to lithium-ion, hydrogen fuel cell, and beyond, there are several different battery types to suit your material handling operations. Getting the most charge for your buck means recognizing how each technology works, including potential limitations. 

One business--and often, even one facility--may need different types of batteries depending on the application, the environmental conditions, and any  sustainability considerations. To help you get a sense of what technology (or combination of technologies) might be best for your application, we created a primer of the primary power solutions, including the pros and cons. Of course, it’s not a substitute for a consultation with a power expert about your particular facility and situation, but it should help give you an overview of your options.

Lead acid 

Lead-acid batteries are as traditional as they come. Developed in the 1850s, they have been the go-to pick for many industry applications, including material handling. Does that make them the most ideal choice for modern operations? Let’s dig in.

First, it helps to understand that lead acid batteries are available in both flat plate or tubular plate models. In a flat plate lead acid battery, conductive positive plates are arranged in a grid-like honeycomb structure and generate energy via chemical reactions between lead and sulphuric acid. Flat plate models are very resistant to higher charge rates.  In short, the faster you charge flat-plate models, the less life you’ll get from the battery.  In most cases, flat plate batteries remain a great option for small one-shift operations, especially where heavy loads are being lifted.

Tubular batteries vary from flat plate batteries in the way the positive plate structure is designed.  Rather than a grid-like honeycomb structure, tubular batteries have spines extending vertically down into the electrolyte. These spines are surrounded by a cylindrical or square casing filled with active material to form tubes. . This design provides more surface area for the lead in the positive plates to  interact with the acidic electrolyte,  resulting in a slightly higher battery capacity versus a comparable flat plate battery of the same model. In addition to about a 15% increase in battery capacity, the tubular design is slightly more efficient than the flat plate design at accepting a charge.

All things considered, the differences between flat and tubular plate lead acid batteries are nominal. Ahead are some commonalities that all lead acid battery models share:

• Cost: At first glance, lead acid batteries are the most cost-effective battery option on the market.  Tubular batteries are about 10% more expensive than their flat plate lead acid counterparts. However, one must also consider the costs associated with the required battery-charging rooms and other maintenance requirements (see below).  Generally, the procurement cost of a lead acid battery, whether flat plate or tubular, represents only about 30% of its total cost of ownership.  How long a lead acid battery will last depends on many factors including quality of the battery, how the battery is used and how often, the user’s charging process and the quality of the charger being used, how well the battery is maintained, and the application environment (both heat and cold significantly impact the longevity of lead acid batteries).  Most lead acid batteries will provide reliable forklift power for between 1200 to 1800 charge and discharge cycles, or three (3) to seven (7) years depending on all these variables. Some very light usage applications might even have well-maintained batteries that last for 10 years or more.

• Charging requirements: Standard lead acid batteries must be charged at a slower rate than the alternatives, with a charging efficiency in the 75% range depending on the charger technology and the health of the battery. This means the amount of electricity you’re paying for is not the same amount that ends up in the battery itself. This inefficiency in the charging process creates  heat and necessitates a prolonged cooling period between uses.  Recent advances in charger technology are allowing for faster charge times with lead acid batteries, but many limitations remain including the need for a weekly equalization charge.

• Warehouse footprint: For applications running multiple shifts, lead-acid batteries will probably require a dedicated battery changing room which takes up space and resources. 

• Operational velocity: Because of the relatively inefficient charging and cooling process described above, lead acid batteries can throttle high-velocity material handling operations, which we define as two or three shifts. On the other hand, smaller, low forklift usage operations are often prime candidates for lead acid batteries.

• Maintenance: Generally speaking, lead-acid batteries require watering at least every two weeks to replenish the hydrogen lost during the gassing process. Moreover, they can only be watered when fully charged. This can be difficult for most operations to keep up with, and while maintenance can be outsourced to a third-party, this is an additional expense. That said, it’s far less costly to outsource preventative maintenance than let it fall by the wayside and shorten your battery life.

• Safety: One safety concern with lead acid batteries is the potential for exposing workers to harmful lead and powerful sulfuric acid. Improper watering can cause acid leakage, which  could result in employee injuries or facility damage. And, while many changing rooms have lifts, there’s always an element of risk when hoisting batteries weighing thousands of pounds  in the air to complete battery swaps.

• Environmental: Lead-acid batteries have the distinction of being one of the most recycled consumer products in the world. They are more than 99% recyclable, and are often re-manufactured into new batteries. Other types of batteries may catch up in the future, but currently, lead acid leads the pack in terms of ease of recyclability.

Lithium

Lithium batteries for forklifts are available in two main types: nickel manganese cobalt oxide (NMC) batteries and lithium iron phosphate batteries (LiFePO 4). The pros and cons of each type vary by application, but in general, lithium-ion batteries offer the following characteristics:

• Cost: The up-front cost of lithium ion batteries is higher than other battery technologies. That said, prices are coming down as the technology evolves, and the fact they require zero maintenance requirements means  they could potentially be the most cost-effective option for some higher velocity operations.  Lithium ion batteries deliver about twice the power over their life when compared with lead acid batteries, or about 3000 total cycles.

• Charging requirements: A fully depleted lithium battery can be 100% charged and ready to go within an hour if the power system is engineered optimally. Unlike with lead acid batteries, the charging process with lithium batteries is extremely efficient and does not generate any significant heat.  This allows batteries to be constantly fast-charged without any adverse impacts on the batteries.    Unlike lead acid batteries, lithium batteries do not require a weekly equalization charge.

• Operational velocity: Because of the relatively inefficient charging and cooling process described above, lead acid batteries can throttle high-velocity material handling operations, which we define as two or three shifts. On the other hand, smaller, low forklift usage operations are often prime candidates for lead acid batteries.

• Maintenance: Lithium batteries are essentially maintenance-free, offering financial and logistical advantages.  Like anything with electronic components though, some maintenance and overall fleet management is strongly recommended to optimize a lithium ion power system. 

• Safety: The lithium batteries designed for forklifts are generally very safe to use because the chemistries are significantly more stable than some other lithium chemistries you may have heard stories about. However, an on-board smart management system is required to monitor each cell individually and ensure there are no imbalances or overheating issues. At extreme temperatures, thermal runaway can cause lithium fires that are difficult to put out. These incidents are extremely rare thanks to the sophisticated internal control system which comes standard on almost all lithium batteries on the market today in the material handling space.

• Environment: While lithium ion batteries are recyclable, the cost of doing so  is significantly more expensive than with lead acid; as a result, it can be hard to find a facility that recycles them and some lithium battery manufacturers charge a fee for the return of an old lithium battery. On the upside, once a lithium battery has degraded to the point where it might not make sense in its intended application, it can still be useful in other applications, such as back-up power.   As lithium ion is becoming the modern solution for transportation electrification, major advancements in the recycling process are inevitable.

TPPL

Thin Plate Pure Lead, or TPPL, batteries are an advanced form of absorbed glass mat (AGM) batteries.  In regard to performance and capacity, they are an enhanced version of lead acid technology requiring less maintenance.

• Cost: TPPL batteries are about 30% more expensive than lead acid batteries but cost less up-front than lithium ion.  The life expectancy of a TPPL battery is two (2) to four (4) years, again depending on many application-specific variables.

• Charging:TPPL batteries can be charged much faster than standard lead acid batteries, but not as fast as lithium ion batteries. One key thing to remember with TPPL technology is that the batteries can only be discharged down to about 40%before their warranty is voided. As such, the ideal applications for TPPL technology are operations with plenty of opportunities to plug up to a charger.   The deeper a TPPL battery is discharged between charging, the lower the life expectancy of the battery.  In fact, most TPPL batteries have an on-board alarm system to notify operators when plugging up to a charger is required. While the charging efficiency with TPPL batteries is significantly better than with lead acid at about 85%, it is a less efficient process than with lithium ion.

• Maintenance: TPPL batteries don’t require watering or weekly equalization like lead acid batteries. However, they do need to be brought up to a full state of charge at least once weekly and they will need to be periodically checked for cell imbalances.  Unlike standard lead acid batteries, TPPL batteries have very low self-discharge rates so they can be stored fully charged for long periods without any adverse impacts on the battery.

• Operational velocity:TPPL batteries can be a great solution for light-to-medium usage one or two-shift operations where production or break schedules allow for plugging up often, but they might not be a ‘blanket solution’ for higher-velocity operations.   The primary limiting factor with TPPL batteries in more demanding applications is the inability to discharge these batteries below 40% state of charge (SOC).

• Resilience: TPPL models are much more resilient to heat and cold than traditional lead acid batteries, but extreme heat and cold should still be avoided.  Repeated over-discharging will also cause premature battery failure.

• Safety: TPPL batteries are as safe, and in many cases safer, than lead acid batteries..  This is because TPPL batteries are designed to be opportunity or fast charged (no battery changing required) and effectively maintenance-free.

• Environment: Much like lead acid batteries TPPL batteries are almost 100% recyclable. There is also near-zero gassing with TPPL batteries.

Hydrogen Fuel Cell

Hydrogen fuel cells are picking up traction in electric vehicle manufacturing and extreme -velocity material handling operations, especially with leading companies like Amazon. In a nutshell, they work by using liquid hydrogen fuel to spark an electrochemical process that generates electricity, heat, and water. Additional characteristics include:

• Environmental: Hydrogen fuel cell batteries are arguably the most environmentally friendly of today’s battery technologies as they require only hydrogen fuel, a clean and renewable resource.  The only byproduct of the energy generation process is water.

• Operational velocity: With hydrogen fuel cell power, fully refilling the tank can be completed in about three (3) minutes.  This makes hydrogen fuel cells an excellent choice for operations wanting to eliminate battery-swapping and where available charging time is so extremely limited that lithium ion or TPPL will not work.

• Cost:  Hydrogen fuel must be stored at the facility for equipment refills and, much like natural gas is delivered to gas stations, fuel stores on-site must be replenished.  The on-location infrastructure requirements for a fuel cell system can be very costly, and the fuel itself is expensive.  Because of the cost, hydrogen fuel cells are used mostly in high-velocity 24/7 operations where the ROI really makes sense.

• Safety: Hydrogen gas is extremely flammable. Therefore, there are limitations as to where facilities utilizing hydrogen fuel cells can be built. That's not to say hydrogen fuel cells are unsafe, but they do require extra safety preparations and considerations. Incidents involving hydrogen fuel cells have been extremely rare and it is considered overall to be a very safe option for powering material handling fleets.

Each to their own solution

There are no one-size-fits-all strategies for forklift power. Factors such as warehouse volume, operational specifics, size, budget, environmental and safety concerns, and time constraints must all be a factor in engineering the best solution. Moreover, your facility’s ideal power solution may involve several different forklift power types combined together as a hybrid solution depending on where (and when) you need power.

Be wary of those who aren’t willing to talk through the pros and cons of the many available options for electric forklift power.  No power system is perfect but working with the right industry experts can help you make a well-reasoned decision about which power solution is best for you. At Concentric we understand that every power technology on the market today has its advantages and disadvantages, and the only way to engineer the best solution is to fully understand your operation and future goals. That’s why  Concentric will not advocate for a specific power solution before conducting a comprehensive operational assessment including an on-site forklift and energy usage study, maintenance practice reviews, interviews with key personnel, inventory and performance evaluation of current fleet, application observations, time studies, and consideration of future needs.