Objective:  Battery chargers and charging requirements

In today’s world of active consumers, many of whom depend on their mobility equipment for daily activities and long-distance use, a technician’s job can be quite challenging.

A technician’s responsibility doesn’t always stop at conducting regular maintenance and repairs. Proper charger sizing and correct diagnosis of battery problems confirming the need for new batteries and/or the reason for battery failure can make all the difference in how mobility equipment will operate and provide dependability long term.

Charging your mobility batteries

There are industry standards that battery chargers used in mobility equipment must meet to ensure proper battery charging. These standards are established by the American National Standards Institute and the Rehabilitation Engineering and Assistive Technology Society of North America.

This standard requires that the battery chargers must have a suitable output voltage and current to recharge fully discharged batteries to at least 80% of the energy that was removed within an eight-hour period. Utilizing the correct size charger for battery size and technology is required to meet this standard, without the risk of under- or over-charging mobility equipment batteries.

How often should I charge my batteries?

If the mobility equipment is used daily, batteries should be charged for a minimum of eight hours every night. For daily long-distance users, a 12-hour charge at least once a week is recommended to prevent potential sulfation buildup on the plates due to potential chronic undercharging that may occur daily. (See Figure 1) If the power mobility equipment is only used occasionally or in storage, the batteries should be fully charged for a minimum of eight hours once per week.

 

Figure 1: Stages of Sulfation

Why type of charger do I have?

Depending on the mobility equipment model, there are two types of chargers used. One is the chargers that will completely shut off after each charge cycle and will not restart a new charge cycle until they are “reset.” Resetting is completed by unplugging the charger from the power source and then plugging it back in to begin a new charge cycle. Another type of charger will continuously monitor the battery’s state of charge and automatically turn on and off, as needed, to maintain a full charge while the charger is in use. Therefore, it can be misleading to assume that if mobility batteries are plugged in while being stored the batteries are always being charged.      

You should confirm the type of charger the mobility equipment uses prior to placing mobility equipment in long-term storage or advising the consumer of proper charging habits.

Always utilize an authorized mobility equipment repair center for your replacement or secondary charger to make sure you are not only acquiring the correct charger size for your mobility equipment but also:

Other factors to be considered:

Battery charger information  

Most mobility chargers have built-in protections that will limit their ability to begin a charge cycle if the batteries are at a very low voltage threshold, generally under 18 combined volts for a pair. This will cause the charger to appear to be charging when nothing is happening. Batteries that are severely discharged can often be recovered but may require individual charging with a 12-volt low-amp charger (not) designed with a low voltage cutoff such as a trickle charger commonly used for automotive batteries. Using a charger not specifically designed for mobility batteries to recover deeply discharged batteries is something only a trained technician should undertake.

When using a non-VRLA specific charger on GEL or AGM batteries, the voltage should be carefully monitored, and the batteries should be returned to the chair’s charger to finish the charge cycle once the voltage of each battery reaches around 11 volts. Continuing use of a non-VRLA charger to finish charging GEL or AGM batteries could result in over-charging the batteries including permanent dry-out and dangerous excessive gassing.  

Figure 2: Rippled battery example

Constant undercharging can be foremost a result of lower runtime, meaning the batteries will not hold their full charge for as long they did when installed brand new. This can result in permanent sulfation on the plates and will quickly diminish the battery’s ability to fully charge as well as maintain their original capacity and runtime, resulting not only in a shorter runtime but also a shortened overall battery life. Chronic undercharging can sometimes be physically noticeable by the battery case appearing concaved or rippled.  (See Figure 2)

In most cases this also results in batteries reading very low voltage, many times due to extended storage of the batteries for long periods of time without proper charging.   

Most VRLA AGM and GEL batteries should have a charge cut-off voltage no higher than 29.20 volts for a pair, or 14.60 volts individually.

This cut off voltage is considered a surface charge and although required to bring a lead battery to full charge, the battery’s voltage will reduce once the battery sits for approximately 24 hours or has a load placed on the battery. A fully charged battery without a surface charge should level out at approximately 12.80 volts. 

A battery with a lower voltage reading reflects a various degree of discharge with sulfation remaining on the plates.  

Figure 3: Open Circuit Voltage Chart

(See Figure 3)

As stated earlier, ANSI and RESNA standards require the battery charger to recharge the batteries to at least 80% of the energy that was removed within eight hours. Depending on the size of the batteries and the charger, it can sometimes take 12 hours to fully charge a lead battery, even when using the correct charger size. If 12 hours of charge cannot be achieved daily, then at minimum the batteries should be allowed to be charged for 12 hours once a week. If this recommendation is not followed, the batteries could experience chronic undercharge and result in permanent damage.

There is technology available in some complex rehab equipment to determine if a battery failure might be due to chronic under-charging. Many newer power chairs have built-in systems that allow the user and the supplier to review the battery charging history remotely.

In addition, consumers of some mobility equipment can now monitor charging habits via a wireless connection through a phone app. This helps technicians quickly diagnose battery problems associated with chronic undercharging versus possible issues with the chair’s charger and/or electrical components. 

Figure 4: Bloated Battery Examples

Although under-charging is the most common concern with mobility batteries, over-charging by using a charger that is too large by output amps or a charger that develops an issue with age or physical damage can also be problematic. Although there will be a reduced recharge time when using a larger amperage output charger than originally provided with the equipment when purchased new, this can cause permanent internal damage to the batteries that can drive out all the electrolyte, permanently destroying the battery. This damage is irreversible and can be often noticeable by the smell of sulfur while charging and the battery case’s expansion or appearance of being “bloated.” (See Figure 4)

Upon observing either of these conditions, the mobility equipment should not be used until the charger and batteries are investigated. If changes/corrections are not made, the replacement batteries will most likely experience the same conditions soon after charging resumes. Also remember that some consumers will purchase a secondary charger via an online store or other alternative resource that is not through an authorized repair center. This could result in the consumer acquiring and using a charger that is too small or too large for their batteries, resulting in battery problems. Always inquire with the consumer if they are using another charger besides the original charger that they received with their power chair.

Other factors that can cause overheating and permanent damage to VRLA batteries include abuse of equipment (utilizing a light-duty scooter for long-distance outdoor use) and exposing VRLA batteries to high heat. It is important to know that after 30 cumulative days of exposure to temperatures of 92 degrees Fahrenheit or higher, for about one hour per day, will reduce a lead battery’s cycle life by half. Using the wrong batteries for the application can also cause battery life to be reduced, i.e., using a smaller capacity battery than the power chair requires, using a nondeep cycle battery or using an AGM battery when a more robust GEL product may be more suitable for regular outdoor use in high-heat climates.  

Conclusion

It is important that qualified mobility technicians:

Whether it be a Complex Rehab Technology power chair or light-duty scooter, proper charging habits and using the right charger can make a difference in battery reliability, longevity and performance. 

Larry may be reached at larryc@mkbattery.com.

Larry Carter is from Dallas, Texas, and has held several positions with MK Battery since joining the company in 1995. He currently serves as MK’s western regional sales manager and national sales training manager. Carter has worked closely with various home medical equipment providers and provider groups nationwide as a workshop presenter conducting battery training sessions for technicians and Assistive Technology Professionals. Carter has worked within the battery industry for over 42 years with experience in all aspects of lead battery applications and technologies, including but not limited to sealed VRLA (valve regulated lead acid) batteries used in mobility and other critical power applications. Carter is proud that MK Battery has been a reliable and trusted source for quality batteries since 1983, and they remain the preferred battery supplier for many HME providers and manufacturers of power wheelchairs and scooters.

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