Many business operations have facilities that utilize fleets of battery powered vehicles. For example, a warehouse may use a fleet of fork lift trucks to move goods into and out of the warehouse. In some cases, such facilities operate twenty-four hours a day. In such scenarios, battery management to keep batteries charged and vehicles moving becomes a difficult problem.
In the typical warehouse scenario, a worker checks out a vehicle and utilizes that vehicle for his entire shift. As the vehicle must also be used for the next shift, the battery must be changed to allow the vehicle to continue to operate, while the original battery is charged off-line. As a typical charge can take up to 8 hours, to keep a vehicle running for three 8-hour shift requires up to three batteries. In an optimized battery change scenario, it is possible to use less batteries by having the operatives only change batteries when the indicator on the truck indicates a change is required.
This model of management of the batteries is inefficient and expensive. In addition to the cost of the multiple batteries required for each vehicle, there is the additional cost of the equipment and labor required to change the batteries and the lost time while the batteries are being rotated.
To minimize the battery changing problem, some facilities have been moving away from charging the batteries at the end of the shift and moving to “rapid charging” of the batteries. Rapid charging occurs when an operator of one of the vehicles takes a break and connects to a very high rate charger for anywhere from fifteen minutes to half an hour. This process will put enough energy back into the battery such that it can run the vehicle until the next time the operator takes a break, or until the end of the operator's shift. While this method eliminates spare batteries, the rapid charge method has several draw backs. First, it is inefficient from an energy usage point of view, with about 75% of the energy going into the battery and about 25% of the energy being wasted as heat. In addition, the rapid charging tends to shorten the life of the battery dramatically. Using the battery changing scenario, one may expect to get up to seven years life out of a battery, but in a rapid charging scenario, the life expectancy of a battery may be reduced to as little as three years. In addition, it is necessary to manage the break time of the operators by staggering the break time such that a charger is always available when the operator is on break.
Therefore, it would be desirable to provide a new method of managing the battery charging to (a) eliminate battery changing and (b) reduce the problems involved with fast charging.