Electric Wheelchair Future Technology

Selecting the correct battery for a power wheelchair means you need to take a serious look at how you use your chair. Then take a look at the characteristics of the different batteries now on the market. An incorrect selection can leave you stranded either because the battery power was depleted or because the battery was unable to provide the power required to navigate over rough terrain.

The battery is one of the major limiting factors in power wheelchair performance. Manufacturers must design much of the wheelchair around the battery package because of the package’s immense weight and volume.

Batteries will last longer, weigh less and take up less space when battery performance is improved through increased battery life (the number of times the battery can be recharged) and battery capacity (the amount of energy the battery can hold on a single charge). Only then will manufacturers have more options in designing wheelchairs. In turn, this will provide you with a more reliable wheelchair, which has lower maintenance requirements and an extended range.

Manufacturers design power wheelchairs for use with deep-cycle lead-acid batteries. They typically use two deep-cycle lead-acid batteries in series, each producing 12 volts (V), for a total of 24 volts (V). The voltage a battery is able to produce describes the electrical force available to drive the motors. Lead-acid batteries are used because they are readily available, inexpensive, rechargeable and available in sizes appropriate for the power requirements and range requirements of power wheelchairs.

Wheelchair batteries are grouped by size, which is indicated by a standard number. The group size defines the dimensions of the battery as shown in Table A. Three typical deep-cycle lead-acid batteries are shown in Figure A. The ampere-hour rating defines the battery’s capacity. That is, if the power wheelchair runs on 10 amperes and has an ampere-hour rating of 90 Ah, then the power wheelchair will be able to run for nine hours at room temperature. In practice, however, you almost never use your wheelchair continuously nor will you need to completely discharge the battery. The capacity of typical deep-cycle lead-acid batteries ranges from 30 to 90 ampere-hours which translates to 3 to 10 hours of continuous use for a power wheelchair that runs on 10 amperes.

Table A. Standard Power Wheelchair Battery Group Sizes. All dimensions are in inches.

Even though automobiles also use lead-acid batteries, and the size of power wheelchair batteries may seem the same as automobile batteries, automobile batteries cannot be used in power wheelchairs.

• Automobile batteries are known as starter batteries. They are designed to provide large bursts of energy over a short period of time, therefore they are almost never discharged to their full capacity, nor are they designed to be discharged to their full capacity, or to 50 percent of their full capacity for that matter.
• Deep-cycle lead-acid batteries used in powered wheelchairs are designed to be discharged quite deeply, where each discharge cycle utilizes the majority of the battery’s available capacity.

There are two types of lead-acid batteries, wet-cell batteries and gel-cell batteries. Both may be used in power wheelchairs, however, manufacturers typically recommend gel-cell batteries over wet-cell batteries due to environmental and maintenance concerns with wet-cell batteries.

In general, deep-cycle wet-cell lead-acid batteries have a larger capacity (ability to travel a longer distance on a single charge), are able to provide more power, and typically cost less. In one study, a set of power wheelchairs with wet-cell batteries traveled approximately 1.25 times farther than the same set of power wheelchairs with gel-cell batteries. There are two types of wet-cell lead-acid batteries: vented and sealed (a.k.a. maintenance free). Because both have chemicals, neither are allowed on airlines.

• Vented wet-cell batteries have maintenance requirements since one of the components that makes up the battery is water, which tends to evaporate over time. Therefore, water must be added to the battery on a regular basis. Another weakness of vented wet-cell batteries is that the consumer is exposed to the acidic materials whenever the casing is opened to add water. Acidic materials can cause chemical burns on the skin and corrode the wheelchair. Also, chemical spills can occur if vented wet-cell lead-acid batteries are overfilled with water, if boiling occurs due to incorrect charging (typically overcharging) of the battery, or if the battery case is damaged.
• Sealed wet-cell lead-acid batteries are considered a closed system, so maintenance of the water level is not required. However they can still have chemical spill due to boiling or damaged battery cases.

Because of these drawbacks, gel-cell lead-acid batteries were developed. There is no potential for chemical spills and they are maintenance-free. These are the only lead-acid batteries allowed on airlines.

Because of the strengths and weaknesses of both wet-cell and gel-cell lead-acid batteries, it might be appropriate to obtain a set of wet-cell batteries for daily use and a set of gel-cell batteries for travel. Furthermore, if your range and power requirements are not extreme, a gel-cell lead-acid battery might be appropriate for everyday use as well. A comparison of the strengths of the deep-cycle wet-cell lead-acid battery versus the deep-cycle gel-cell lead-acid battery is listed in Table B.

Table B. Strengths of a deep-cycle wet-cell lead-acid battery versus a deep-cycle gel-cell lead-acid battery

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