Lithium or lead-acid for pushbacks?
A safe lithium battery pack for electric pushback tractors. In the article about our self-developed planetary gearbox, we explained what makes the drivetrain for a pushback tractor so efficient, enabling pushback operators to perform 20–25 pushes on a single battery charge. But this efficient drivetrain isn't enough without a high-quality battery pack. The battery pack in the conversion kit for a pushback tractor is built on lithium battery chemistry. But why do we choose lithium over the well-known and trusted lead-acid?
The GSE market has been using electric equipment for quite some time already, for example for belt loaders or passenger stairs. These generally rely on lead-acid batteries. Lead-acid batteries are relatively cheap, easy to install, and widely available. However, the advantages of lead-acid packs don't outweigh the disadvantages of using them to electrify a pushback compared to a lithium pack. Why? Lead-acid packs have the characteristic that relatively little current can be drawn over a shorter period compared to certain lithium packs. Given that the drivetrain for pushback tractors requires relatively high power — compared to the drivetrain of a stair truck or a belt loader — a lead-acid pack simply isn't sufficient. At the end of the day, a pushback still needs to push 92 tonnes of weight.
Even if a deep-cycle traction lead-acid pack were used, that would mean a battery lifespan of around 500 cycles. With 10 to 15 pushes per day, the lead-acid battery — even with good maintenance — would be written off within 2 years.
But why are we saying this? Simply put, we already made this mistake ourselves on behalf of the end user. Our first prototype electric drivetrain for pushback tractors used a lead-acid battery pack. The test data showed that the battery degraded, or in other words, its effective capacity decreased. We also observed that in very high ambient temperatures (>45°C), battery degradation accelerated. Above 45°C may sound exceptionally hot, but on a platform with black asphalt in Southern European regions, that's certainly not unusual!
That's why we developed a lithium pack with an average lifespan of 7–9 years, requiring no maintenance. Compared to lead-acid, this can result in cost savings of between 30% and 50%.
By using lithium, the overall pack can function in high ambient temperatures, as is the case for our customers in Southern Europe. The battery pack can also be heated, allowing it to perform well in areas with very low ambient temperatures (<0°C). And last but certainly not least, the battery chemistry used is LiFeYPO4. This chemistry is characterized by strong resistance to overheating compared to other lithium chemistries, which is why it's considered a safe battery chemistry.
Furthermore, lithium packs make it possible to deploy charging infrastructure at airports more intelligently and effectively. Why? We'll discuss that another time.