Lithium-ion forklift batteries are supposed to last three to five times longer than lead-acid batteries, but warehouse managers are getting a rude awakening when they try to cash in on those eight-year warranties. The batteries are dying in three years, and the manufacturers are denying the warranty claims based on data pulled directly from the battery's internal computer. The culprit is a misunderstanding of Depth of Discharge (DoD).
With old lead-acid batteries, the rule was simple: run it until it's dead, plug it in, and charge it to 100%. If you do that with a high-end lithium-ion forklift battery, you will destroy its capacity in a fraction of its rated lifespan. Lithium-ion batteries age based on charge cycles. Pulling a battery from 100% down to 5% counts as one massive, stressful cycle. Doing this every shift racks up the cycle count incredibly fast, degrading the internal chemistry.
To get the advertised 8,000 to 10,000 cycle lifespan out of a lithium battery, the warehouse must practice "shallow cycling"-typically only discharging the battery down to 20% or 30% before putting it on an opportunity charge during operator breaks. The Battery Management System (BMS) logs every single percentage point of discharge. When a warehouse files a warranty claim for a battery that has lost 30% of its capacity, the manufacturer pulls the BMS data, sees that the warehouse routinely deep-cycled the battery to 5%, and points to the warranty fine print stating that the warranty is voided if the average DoD exceeds a certain threshold. Warehouses are buying million-dollar lithium fleets but running them on 1980s lead-acid charging mentalities, and it's costing them a fortune.
