Warehouse Design – Materials Handling Equipment: lead acid vs lithium ion batteries
Posted on 10th August 2022
For facilities managers and warehouse designers like me the effective use of space and energy is a key concern. That’s why I want to introduce you to the possibilities of lithium ion batteries for powering materials handling equipment (MHE) in warehouses.
You might think this technology is reserved for the new electric car you will soon have on your driveway, but it has huge potential for your workplace as well. The use of lithium ion batteries, coupled with renewable sustainably sourced energy, is an efficient option that would help improve your environmental credentials as you develop your net zero strategy. As your customers become increasingly interested in the carbon footprint of their supply chain this will be an important consideration.
It is also an exciting opportunity to re-evaluate the warehouse design process and I’m going to suggest some operational benefits you might not have thought about. I will also look at layout options and the operating changes you could make to fully benefit from the use of lithium ion batteries in your warehouse operations.
I intend to be thought provoking so hopefully my suggestions will lead to some further discussion. I would appreciate your feedback and comments. As I’m not a qualified electrician, I’m also quite prepared for you to tell me that some of my observations are incorrect, in which case I will be happy to make some changes.
The MHE purchasing decision
The government’s electric vehicle infrastructure strategy has raised the profile of electric vehicles for private and commercial use. Many of us will already own or be looking to buy a new electric or hybrid vehicle in the next few years.
To help us make the best choice of electric vehicle we will carefully consider all fuel types, the different options available to us, where and how we will charge our vehicles, the initial purchase price, and overall running costs. We might even create a spreadsheet to help us justify the decision. You would probably take a similar approach when choosing MHE for your warehouse.
MHE fuel type comparison
There are four main power sources for trucks commonly used in warehouse operations:
LPG (Liquid Petroleum Gas)
lead acid batteries
lithium ion batteries.
Diesel – diesel powered trucks are typically used when operating outside in yards. The diesel will normally be stored in a tank in the yard area which is topped up by an external supplier. Generally, diesel power is used for trucks more than 1.6 ton.
There are a few things to consider when thinking about diesel trucks:
diesel vehicles are quite noisy whilst in operation
diesel equipment creates fumes
generally, the use of diesel equipment can result in grease and grime on the floor and areas of use
modern diesel trucks must meet European regulations on emissions
the cost of fuel.
Still trucks, for example, feature diesel particulate filters (DPFs) to reduce the particulates being emitted.
When considered against LPG trucks:
emissions from diesel trucks are less visible but they are more harmful as they contain higher levels of nitrogen oxide.
When compared to battery powered trucks, diesel powered trucks:
don’t need to be charged
are becoming more expensive to run with increasing fuel costs
have similar performance.
Liquid Petroleum Gas (LPG) – generally used for forklift trucks, LPG power is mostly used when working outside for prolonged hours where operations might require higher speed. LPG is stored in tanks in a safely protected area in an outside yard and will be replenished by an outside supplier.
Considerations when using LPG-powered trucks include:
suitability for limited indoor use
fumes and dust from the motors
whether operation at a higher speed is needed
the cost of fuel.
Compared with battery powered trucks LPG-powered trucks:
don’t need to be charged
cost more to run
have similar performance.
LPG external storage tank
Lead acid batteries – a tried and tested power source used for warehouse trucks, lead acid batteries were originally invented in 1860. Although the technology has been refined the same principle is still used for the batteries most of us use in our non-electric cars.
Considerations when using lead acid battery-powered trucks:
initial purchase cost
time between recharging or battery swapping
cost of recharging
time needed to recharge.
Compared with lithium ion battery-powered trucks, lead acid batteries:
require more energy to charge
require less power*
need to be swapped regularly
require more maintenance
have a shorter life
need to be replaced more frequently
can be recycled.
Lead acid battery charge area
* TH comment: Draw from the electricity supply for lithium ion battery-powered trucks could be up to four times higher if the fleet all charged at the same time: during lunch breaks or at the end of shift, for example. Lithium ion battery chargers require more power compared with lead acid chargers which are designed to charge at a slower rate.
In many instances there will be a spare fully charged lead acid battery waiting to be used. Another factor to consider is that retrofitting an existing site with power for lithium ion battery powered trucks can be very expensive, this needs to be factored into any investment decision. It is also true that setting up a site for lithium ion powered trucks for a new build will also require additional infrastructure and cost.
Lithium ion batteries – generally smaller in capacity and needing more frequent charging than equivalent lead acid batteries, lithium ion batteries might not seem to be suitable for many warehouse applications.
However, when bought lithium ion battery-powered trucks will have a single battery and this is where the subject starts to get really interesting to me as a warehouse designer.
Considerations when using lithium ion battery-powered trucks:
trucks can be supplied with different sized batteries
higher battery costs than equivalent lead acid alternative
optimisation of battery size to suit planned operations and minimise unnecessary costs. This is also true for lead acid battery powered trucks. However, it is vitally important that when designing a system that the battery sizes and chargers are carefully considered.
heavier batteries require more power to move
speed of charging
operations that involve heavy loads such as fully loaded pallets lifted to height will require more power, larger batteries, and more frequent charging
Very Narrow Aisle (VNA) trucks will need a larger battery and a faster charger than required for an order picker, PPT or reach truck
the potential for frequent ‘top up’ charging and smaller batteries suitable for light use trucks and those used infrequently during the day such as powered pallet trucks (PPTs) to unload trailers or order picking trucks.
Toyota PPT lithium ion battery powered trucks
The calculation of working hours, usage and shift patterns is complex. Based on their current analysis of real-world applications Still uses tested results to evaluate the use of lithium ion batteries based on:
their capacity when fully charged (although there are various battery size options to consider)
the discharge rate when being used based on operations which include types of activities and weights lifted, lift heights and travel distances
charging duration and frequency.
And, of course, as operations change over time, it is always best to consider ‘what if’ scenarios such as:
introducing a third shift to operations
changing the number of trucks used on each shift
the impact of high peak demand
the likelihood of short term hire of equipment which will probably be lead acid battery powered, and where it could be charged in the warehouse.
Compared with lead acid battery-powered trucks, lithium ion batteries:
will have a longer life cycle as they can be charged more times before the batteries degrade. It is reported that lithium Ion batteries can last for between 10 to 12 years, whereas lead acid batteries may need replacing after 5 to 6 years*.
when used for multiple shifts will require frequent charges rather than removing and swapping batteries at the start of each shift.
* subject to varying factors such as use and charge frequency, these figures are intended as a guide only.
Lithium ion battery-powered reach trucks
Charging considerations for lead acid and lithium ion batteries
Lead acid trucks are generally charged in a separate part of the warehouse. This area will typically include battery replacement trucks, the chargers, spare batteries, a maintenance area with a limited amount of spares and tooling (also required for lithium ion trucks). The area will also include space for truck charging. Where operational space is at a premium, this is an important consideration.
The area needs a high voltage power supply and must be well ventilated. A health and safety station will also be needed with materials such as eye cleaner and instructions about how to charge and top up lead acid batteries safely.
Larger warehouses might have multiple charging locations depending on their size and how close the chargers can be to employee welfare facilities.
Lead acid – typical charging and maintenance area with battery change trucks
Lead acid battery change truck/tugger
In contrast, lithium ion trucks can be charged anywhere in the warehouse. Gases aren’t emitted during the charging process so charge positions can be strategically located at areas that otherwise would not be considered, making them an attractive option when planning your warehouse design.
Lithium ion truck chargers can be:
Between dock doors – this option is especially suitable for trucks used to unload vehicles. This is sometimes a dead space, which can be easily allocated to truck charging when the docks are inactive.
Lithium ion – schematic of dock charging location in a typical charging and maintenance area
Lithium ion – dock charging locations between bay doors
At rack ends – for order picking trucks or reach trucks used to replenish pick areas or feed reserve pallets this option can make good use of space and improve efficiency. The chargers can even be placed inside the racks at ground level although this would mean that part of the pick face would be lost. Chargers can also be placed at the end of the racks.
Rack end charging stations
TH Comment: positioning a charging point at a rack end will require detailed design and consideration of the warehouse operations. It is possible to locate most trucks at rack ends, but expert advice will be needed about driver access of the trucks, barrier protection, supply of electricity and the charger location.
In aisles – picking or reach trucks could be charged in aisles.
The importance of battery charging footprints
The real impact of different truck charging options is the overall footprint allocated to charging and maintenance. A smaller footprint means you will have more productive storage space in your warehouse.
Still lead acid charging installation
An example lithium ion charging regime
Lithium ion battery-powered trucks rely on regular short top up charges. Some operators will use the trucks for all of their working shift, so they will need a quick charge at every opportunity.
The location of the charge point needs to be convenient for the driver, so ideally the charge points will be located close to break areas or locker rooms for the end of the shift.
The chart below shows the rate of battery discharge over a two shift operation. In this instance lithium Ion batteries are compared to lead acid batteries. The lithium ion batteries discharge more quickly but are smaller. The chart shows how a lithium ion battery will deplete over a typical day with quick top up charges.
Calculation showing battery consumption + charging
The charge locations need to be clearly identified with a defined parking space, suitable Armco barrier protection and a clearly marked out access space. High levels of housekeeping are required to ensure these areas are always kept free from debris, not used as temporary storage locations or drop off points. Drivers must also be trained so they don’t park in other locations and always connect to the charger.
Clearly marked charging location for order picking equipment
Trucks suitable for lithium ion batteries
All truck types used in warehouse operations could be powered by lead acid or lithium ion batteries including order pickers, PPTs, reach trucks, fork lift trucks, and VNA trucks.
A lithium ion powered truck is generally more expensive to buy than its lead acid equivalent. However, the lithium ion truck does not need a spare battery and does not require an additional truck to change the battery. So, in many cases, when you compare both alternatives, the price difference of an overall solution can be a few percent plus or minus.
TH Comment: on a recent project we decided to have a combination of lead acid and lithium ion trucks, with the majority being lithium ion. This allowed for maximum flexibility and provided the most economical solution for the client.
All businesses are looking to improve how they operate, to find ways to reduce their bottom-line costs, and to improve their environmental credentials. Lithium ion powered equipment is not suitable for all warehouse applications but is very well suited to many. They can also help to make better use of space in your warehouse design and other operational improvements can also result from adopting this technology.
Consideration will include the stable supply of lithium, the cost of purchase and lead times for delivery, warehouse design to take full advantage of lithium ion operation, and the electricity supply and infrastructure available for your location.
When considering the total cost of ownership of lithium ion technology, initial costs can be off set against lower maintenance requirements and the fact the additional batteries and battery change trucks are not required and a smaller battery charging footprint. In the longer term there is also the question of adequate provision for recycling of lithium ion batteries at the end of their life. At the moment there isn’t an easily accessible recycling path, so this area might become a problem in coming years.
I would like to thank Still and CAPS Systems who have supported me with some images and advice where required. Still has a range of trucks that can be operated using lithium ion or lead acid batteries. CAPS Systems has helped with some of the technical design aspects relating to charging and specialist electrical design considerations about which I’m not qualified to comment. Both suppliers have been an invaluable source of information and support and I appreciate their input. Please visit their websites and let them know I sent you!
As an independent consultant specialising in warehouse design, I must stay at the forefront of modern technology and equipment. I have no allegiance to these companies although I would be happy to recommend them for inclusion in your shortlist of potential suppliers.
My work for my clients is always impartial and the best interest of my clients is my top priority. If you are considering using lithium ion powered equipment in your operations then an analysis of your current operation and assessment of alternative concepts should be assessed by impartial, independent experts.
Please do not hesitate to ask for any advice. I would be very happy to have an initial no obligation chat or, if required, provide a quotation for any assistance.
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