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This month, Clinical Corner will re-visit the topic of batteries in power wheelchairs. This topic was first addressed in a 2012 blog post, De-mystifying Power Wheelchairs: Batteries and Motors. This month, Clinical Corner will review and update the information first presented in 2012 regarding batteries. Batteries are an important consideration in power wheelchairs as they provide the power required to operate the system.
Battery Sizes
The batteries of a power wheelchair are like the "gas tank" of a vehicle. The batteries provide the energy to drive the electric wheelchair. Wheelchair batteries, like gas tanks on vehicles, come in different sizes and hold different capacities of energy. There are 3 common sizes of wheelchair batteries: Group 22NF, Group 34, and Group 24.
Group 22NF batteries are smaller and lighter in weight than Group 34 and Group 24 batteries. Being lighter and smaller helps to decrease the overall weight and width of the power wheelchair. However, the drawback is that less power is available in the Group 22NF batteries to operate the power wheelchair. Group 22NF batteries are a good choice for use on basic power wheelchairs that will be used primarily in indoor environments.
Group 34 batteries are next in size when comparing power available and weight of the 3 common battery sizes. The Group 34 batteries offer more capacity than the Group 22NF batteries, but less than the Group 24 batteries. It is estimated that the Group 34 batteries have a 10% greater range than the Group 22NF batteries. A benefit of the Group 34 batteries is that they offer a lower profile than the Group 22NF and Group 24 batteries, due to their shape. The lower profile of the Group 34 batteries allows for lower seat-to-floor heights on the power wheelchairs than the other battery sizes.
Group 24 batteries have the greatest capacity of the three sizes, providing more power to operate the electric wheelchair. Group 24 batteries are heavier than Group 22NF and Group 34 batteries, which makes the overall weight of the power wheelchair heavier when such batteries are used. The width of power wheelchairs can be the same whether using Group 34 or Group 24 batteries. Group 24 batteries are a good choice for power wheelchairs that will be used in outdoor environments and/or that have other systems, such as power tilt system, operating from the power of the battery, and for individuals who do not require the lowest possible seat to floor height.
Battery Types
Just as there are choices in batteries sizes, there are also choices in types of batteries. Gel batteries and AGM (Absorbent Glass Mat) batteries can be used in wheelchairs. The difference between them relates to the number of times the set of batteries can be charged and the distance that an individual can use their wheelchair on a single charge. Price may be another factor in the choice.
Gel batteries can be re-charged a higher number of times than AGM batteries, which means that they will not require replacing as often as AGM batteries. The expected life of a gel battery can be much greater than AGM batteries. AGM batteries, however, will offer greater daily range than gel batteries. This means than an individual can drive further on a single charge in a day, with some estimates being as much as 20% greater daily range with AGM batteries than gel batteries.
It is difficult to estimate precisely how far an individual may go on a single battery charge. So many factors go into the draw on the batteries, such as weights of the individual and power wheelchair, type of motor, temperature and terrain of the environment in which the wheelchair is being used, programming parameters (e.g., percent of power available), and operation of other systems through the batteries.
Battery Chargers
Sometimes choice is offered in the number of amps available in the battery charger so it is helpful to understand possible different options. For example, there are 10 amp battery chargers and 8 amp battery chargers that are available for Group 34 batteries. The 10 amp charger offers a faster charging time for the batteries, with it being 45% faster than traditional 8 amp chargers. Whereas a standard battery charger would be included in the cost of the set of batteries from a wheelchair manufacturer, an optional higher amp battery charger could be offered at an additional cost.
Summary
This month's Clinical Corner article has focused on the power that drives electric wheelchairs – batteries. The size of the batteries and the choice between gel and AGM will have a direct impact on the range that an individual can drive on a single charge. If an option is given on the order form for battery chargers, the choice will have a direct effect on how quickly the batteries will return to a full charge. All of this has an effect on function for an individual.
Sheilagh Sherman, BA, BHScOT, MHM, OT Reg. (Ont.)
Clinical Education Manager
Sunrise Medical Canada
Note: The content of this article is not meant to be prescriptive; rather, it is meant as a general resource for clinicians to then use clinical reasoning skills to determine optimal seating and mobility solutions for individual clients. Sheilagh is unable to answer questions from members of the general public. Members of the general public are directed to their own therapists or other health care professionals to ask questions regarding seating and mobility needs.
This article is © Sunrise Medical, Inc., 2019 and cannot be copied, distributed, or otherwise reproduced in whole or in part without the express written permission of Sunrise Medical Canada.