If you use a power chair or assist, the limiting factor is battery life
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No matter what type of mobility device you use, the allure of being able to go farther and faster with less effort and toll on your body is always appealing. If you use a power chair or assist, the limiting factor is battery life. Thankfully, advances in battery technology are extending the range of wheelchairs, allowing their users more freedom to explore than ever before.

Switched On

Ian Mackay has completed two 300-mile border-to-border crossings of Washington state in his wheelchair, first going north to south and then east to west. Although lengthy adventures like these are nothing new for him, his journeys have a twist.

A C2 quad, Mackay tackles the terrain, which includes long climbs and descents over steep passes, in his 3-year-old Invacare TDX. Remarkably, he averages 40 miles a day without stopping to recharge. The secret to his long-distance success is that he supplements his lead-acid batteries with a lithium-ion one mounted on a tray behind his chair. A friend custom-built a wiring harness that allows Mackay to toggle between the two types with the flip of a switch.

The lithium-ion battery on the back of Ian Mackay’s chair gives him the power to climb long-grades.

The lithium-ion battery on the back of Ian Mackay’s chair gives him the power to climb long-grades.

Mackay’s long-distance trips double as fundraisers for Ian’s Ride, his nonprofit foundation dedicated to increasing outdoor accessibility. They also provide a perfect illustration of the differences between lithium-ion and lead-acid batteries.

His two group-24 sealed lead-acid batteries are identical to what most power chair users rely on. Thanks in part to his chair’s gearless, brushless motors, Mackay estimates he gets 30 miles on one charge, which is about the same distance he expects from his supplemental 24-volt, 75-amp-hour, lithium-ion marine battery — but the similarities stop there. The lithium-ion one weighs 70% less than its lead acid counterparts. Additionally, the two power sources deliver their charges very differently.

Lithium-ion batteries maintain max power output until they are depleted, whereas lead-acids put out less power as they near empty, resulting in a noticeable slowing of the chair. “In my experience, the lithium-ion battery gives me the same range as lead-acid. But because it puts out full power until it quits, it gives me an average of 1 mile per hour extra speed over a course of 20 miles,” says Mackay.

Everyone who uses a power chair probably isn’t going to need the ability to go up to 50 or 60 miles without recharging like Mackay, but having more options is always a good thing and bodes well for the future. “My setup gives me the flexibility to explore the outdoors as much as I want for as long as I want, and that flexibility is something we should all have,” he says.

The Lowdown on Lithium

Lithium batteries aren’t exactly new, but they are powering a growing number of power-assists that are improving the lives of their users. Although there are several types of lithium batteries, the type used in most mobility devices, as well as power tools and approximately 90% of electronic-assist bikes, is lithium-ion. These batteries consist of individual cells, such as the 18650, which looks like a slightly-bigger AA battery. Larger lithium-ion batteries consist of multiple cells in a management system known as a battery pack. These can range in size from small for an e-bike to large enough for a Tesla car.

Christian Bagg took advantage of the ability to customize the size of the pack while designing the Bowhead Reach adaptive adventure cycle.  “When we started Bowhead, we would get our lithium-ions by taking apart packs from crashed Tesla cars that had 2,000 cells in them,” says Bagg, a T8 para. “In a Bowhead Reach we use two battery packs with 50 cells in each.”

Lithium-ion’s blend of power and reduced size and weight, combined with more efficient motors, also helped to enable the development of devices like the SmartDrive, Yamaha NAVIONE, Twion wheels and the steerable Firefly.

The primary disadvantage of lithium-ion batteries for standard power chair design use is that they are significantly more expensive than lead-acid and require a complicated charger that controls how much and for how long it charges. Also, because of concerns about lithium-based batteries catching fire, you have to get a FAA waiver, or the battery has to be below a certain size, to take it on an airplane.

Mackay was initially hesitant about lithium-ion batteries because of reports that they could get hot enough to catch fire. He researched and found that was more of a problem with earlier ones, and that if there was any danger it would be during charging, not when it is sitting or in use. Also, the fire problem was primarily limited to one type of cellphone that didn’t have very good chargers.

If you’re wondering why more power chairs don’t switch to lithium-ion, experts say it’s simple: lead-acid batteries work well. And, the bulkier, heavier size of lead-acid batteries gives power chairs a low center of gravity, which can be desirable for stability.

On the flip side, the desire to shed pounds led the designers of the new iBOT to ditch the nickel cadmium used in the original. “Switching from ni-cad to lithium-ion provides a significant weight reduction,” says Luke Merrow, CEO of Mobius Mobility. “Because the iBOT is a dynamic chair, weight is a very big issue. The lighter the machine is, the more responsive it is to the human.”

The iBOT uses four lithium-ion battery packs, which lasts for about 17.4 miles. Users can add two more packs for an expanded range, and the iBot is still within the size and wattage limits for commercial airlines.


Comparison of Products Mentioned in this Article:

Devices Powered with Unique Lithium Batteries

RANGE MAX SPEED WEIGHT
IBOT 17.4 MILES 6.7 MPH 4.4 LBS x
4 battery packs=
17.6
FIREFLY 15 MILES 12 MPH 3
BOWHEAD REACH
(80 VOLT)
15-20 MILES 20 MPH 13

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Comparison of Power Chair Batteries Mentioned in this Article

GROUP 24 LEAD-ACID LITHIUM-ION
RANGE 21 MILES 21 MILES
MAX SPEED 7.5 MPH 7.5 MPH
WEIGHT 52 LBS x 2 batteries = 104 LBS 31 LBS
APPROX. RETAIL $305 per battery x 2 = $610 $1,400
FUN FACT Weight keeps center of gravity low, helping with stability. Chair performance slows when charge is run down to a certain level. Delivers full power until completely empty then quits. This results in approximately 1 mph extra speed over a full 21 miles compared to lead-acid.

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Power Assist: Taking Back the Trails

Beyond wheelchairs, lithium-ion batteries and improvements in motors are also upgrading adaptive recreation. Their smaller size and the ability to add packs for more power makes them perfectly suited for the needs of outdoor enthusiasts looking to tackle increasingly-tougher terrain.

The outdoors opened up for Topher Downham when he added an E-BikeKit power assist unit with a lithium-ion battery to his handcycle. Downham, the outreach coordinator for Boulder, Colorado’s Open Space and Mountain Parks, is in his 25th year as C6-7 complete quad. He has a Freedom Ryder that he purchased used for $500. “I rode it for years and enjoyed it, but I was much slower than my nondisabled friends, and couldn’t go anywhere near the distance they did. Plus, after a ride I’d be wiped out.”

The E-BikeKit he later added has a range of 42 miles and top speed of 20 mph. “With the E-BikeKit, I can keep up with my nondisabled friends on long rides and still have energy to go have a beer afterward,” he says. “Also, it’s safer. With my level injury I don’t sweat, and if I’m riding way out there and start overheating, I can just hit the thumb throttle to go fast enough for a cooling breeze and make it home safely.”

Howard Kramer and Topher Downham ride NUKE off-road mountain handcycles with power assist on a trail above Boulder, Colorado.

Howard Kramer and Topher Downham ride NUKE off-road mountain handcycles with power assist on a trail above Boulder, Colorado. Photo by Dakota Anderson.

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Open Space and Mountain Parks bought three NUKE off-road handcycles and later converted two of them to power assist. “Prior to power assist, it was tough to get new SCIs interested in the off-road handcycles because it’s difficult unless you are in good shape,” says Downham.  “With power assist, it is a different ballgame. People who haven’t been on a bike path or trail since their injury start off kind of tentative. By the end of the day they are doing river crossings, and they have these shit-eating grins on their faces that say, ‘Yeah, I’m back, my life isn’t over!’ That makes it for me — reaching one more person and showing them the possibilities.”

“With power assist, instead of having to ride a chair lift up a mountain bike resort to enjoy riding down single track, or struggling to peddle a mile and calling it quits, I can hop on, go biking with my friends, and get a great workout,” he adds.

Speaking from experience, I can attest that power-assist add-ons are amazing for paraplegics as well. I rode off-road handcycles for well over a decade, and it was a blast, but even on mild uphills my speed was reduced to a walk, and a long ride wiped me out. Now I use a Bafang e-bike kit on my Reactive Adaptations Bomber handcycle. Not only does it enable me to ride with my nondisabled friends, but it also lets me take Killy, my German shepherd, on the 2-mile, 1,000-foot descent to, and climb back up from, our favorite swimming hole on the American River. It provides a serious workout without putting undue strain on my aging shoulders.

While lead-acid batteries remain an excellent and more affordable energy source for most power chairs, it is exciting to see the innovation inspired by lithium-ion batteries. Hopefully they will continue to make it easier to go farther and faster for a long time to come.

Many thanks to Rory Cooper, founder and director of the Human Engineering Research Laboratories at the University of Pittsburgh, for his input and expertise on power sources for mobility devices.