Battery Questions Answered


Batteries are the heart of every power wheelchair and scooter.  They
"pump" the electricity to the motors, and the sophisticated
electronics used by todays power chairs and scooters closely
measure their output voltage.  If it drops before a certain level, the
electronics shut down to prevent damage.

Depending on the electronics, you may or may not get an error message
when this happens.  But over 90% of the service calls we get involving
electronic problems are nothing more than either wrong, defective,
un(der)charged, or "used up" batteries.  Most wheelchair manufacturers
will not even talk to the service technician to troubleshoot a problem
until s/he determines that the batteries are good.  Some insist that
new batteries be installed (they can be removed after the chair or
scooter is running correctly and it is determined the old batteries are
not to blame) whenever there is an electrical problem to see if the 
problem goes away or changes.

Most modern power chairs and scooters have (2) 12 volt batteries wired
in series to create a 24 volt system.  The wiring may be obvious (the
positive terminal of one battery connected to the negative of the
other), or it may be done internally in the equipment's electronics
(usually the case for scooters and not rare in some power chairs).  To
the batteries, it is like having one large battery- and because of
that if one battery is bad (or even weak), it will bring the other
battery "down".  It is very important to always replace the 2 batteries 
as a set at the same time.


The manufacturer of the equipment will advertise a range that the
wheelchair or scooter can go between charges.  Usually they will word
it as: "between ## and ## miles between charges".  My advice is to take
the lower of the 2 numbers and make that the maximum range.

Further, the range is qualified to a (usually) 170 pound user on
level ground at 70` temperature.  This is a constant in the industry.
And the manufacturer will (obviously) use good quality batteries when
computing the range.

As the batteries age, that range will decrease.  Given enough time, the range
will become essentially zero miles.  Usually after one year, the range has
decreased enough that the same "average" user can't go a full day without
recharging.  Obviously a person who is only going several hundred yards a day
indoors will have a greater range than an active user traveling great distances
outdoors (example: a college student "on campus" going between classes).

Several ultra-small scooters and wheelchairs have come on the market.  These
tout their light weight as their selling point.  Understand that most of these
have very small batteries.  These batteries will have both a much shorter range
between charges AND a much shorter life between replacement!  A general
rule is that the shorter the advertised range, the shorter the life of the
battery before replacement.


There is no "memory effect" in wheelchair batteries.  If you drive the 
equipment that day, charge it that night.  The batteries will not develop 
a memory, and if you were provided with poor quality or "automotive" 
batteries, doing so may buy you a little longer life.


Quite simply, they do not work.  Automotive batteries are designed to
put a large amount of power out in a very short amount of time.  They
are also designed to deal with very high extremes of temperature under
the hood of a car (from below zero on a cold winter night up north
with the wind blowing, to over 250 degrees under the hood of a car
stopped on I95 in a rush hour traffic jam).  An automotive battery
does its job for maybe a minute or so while the starter is engaged.
Then the automobile's charging system "kicks in" when the engine is
running and recharges the battery.  The battery must also be designed
to withstand the "pressure" of the charging system against it for many
hours of driving while the battery is fully charged.  Because the car
battery is really only used for a minute or so at a time (the
electrical system may "borrow" from the battery at a stop light or in
stuck traffic if a lot of accessories are running, but this is minimal
and non-existent when the car is moving), it can last a few years or

Batteries for wheelchairs and scooters have the opposite problem.  The
temperature requirements and output (compared to an automobile
battery) are minimal, but the battery must go from fully charged (in
the morning right off the charger) and power the wheelchair/scooter
all day without recharging- and without going slower as the charge
diminishes (within reason).  The chair is then put on a charger and
the battery is recharged slowly, usually over night.  The term for a
battery going from fully charged to discharged to fully charged again
is a "cycle",  and because the battery is going to discharge quite a
bit, the term for a battery that can do this over and over again is
"deep cycle battery".  Automobile batteries are "high output
batteries", wheelchair batteries are "deep cycle batteries".  Most
deep cycle batteries are good for 350 to 500 "cycles"- figure a year
of usage.  Your mileage may vary.

To compound the problem, a lot of places that sell batteries simply
don't understand this concept.  Others simply don't care.  And it is
impossible to tell a deep cycle battery from an automotive battery by
looking at it (except for the label, which many times is put on by the
battery supplier at the time of sale).  As a dealer, I have had
battery suppliers deliver to me automotive batteries with deep cycle
labels on them.  We find out they are the wrong batteries a month or
so later when they start to fail (and the customer is very angry at
that time).  The battery company may provide you with a replacement
warranty- usually pro-rated, but even with "full free replacement",
you will not be reimbursed for your inconvenience, lack of use of the
equipment while waiting for replacement batteries, or any service
call you encounter trying to determine that the batteries are
defective/non-deep cycle (assumes you didn't get your batteries from 
the company who is now diagnosing the electrical problem).  Many 
battery companies will insist the batteries "test" fine when in fact 
they cannot hold a charge for a full day (because they are "starting" 
vs "deep cycle" batteries.

Automobile and deep cycle batteries come in the exact same sizes (see
size section).  This just compounds the problem.  And scooters users
(that generally use a smaller battery) now have to contend with 2
additional problems:  the "garden tractor" starting battery (wet) and
the "emergency light" battery (gel- see "wet vs gel" section).  These
aren't generally considered automotive batteries (due to their size),
but they are not deep cycle either.  But the size is the same as the
majority of scooter batteries (U-1).  Some companies selling scooter
batteries mail order have shipped emergency lighting batteries as deep

WET VS "GEL" (Sealed Lead Acid)

Batteries appropriate for wheelchairs and scooters come in different
sizes and in the past came in two "types": liquid or sealed lead acid.
Sealed lead acid batteries can be manufactured with a gel inside to hold
the acid in place (it's mixed with the gel), or they may have fiberglass
matting between the plates to hold the acid in place.  Because gel
batteries were the first kinds of sealed lead acid batteries, many people,
including dealers, call all non-spillable batteries "gel cells", and
the ones with the fiberglass matting "sealed lead acid".  I am using
"sealed lead acid" (the correct term) to encompass all non-spillable
batteries as their characteristics to the end user, care, and charging
procedures are identical.  Today, all wheelchairs and scooters should if
at all possible have the non-spillable sealed lead acid batteries
installed instead of wet batteries.  The damage cause by spilled acid
is expensive, and the "gassing" of wet batteries causes both damage to
the wiring/electronics/frame of the chair and poses a possible (albiet
very slight) chance of explosion.  Battery connections loosen when
corrosion is present- causing more (expensive) service calls.

Sealed lead acid batteries do cost more (more expensive to produce),
and in the past did not last nearly as long as properly maintained
liquid deep cycle batteries, and do require a special battery charger.
As their output and range is less than sealed lead acid batteries, some
mobility manufacturers did not recommend them for their chairs.
Manufacturers now recognize the benefits of sealed lead acid
batteries and I don't know of any wheelchair/scooter manufacturer now
selling in the USA that is not providing the "correct" charger as standard
equipment.  One manufacturer (Invacare) has even started putting larger
battery boxes on some of their power chairs to compensate for the lower
range/capacity of sealed lead acid batteries. Given that the life of
a sealed lead acid battery now is almost as long as a wet battery, the
advantages of using a nonspillable battery is certainly worth the
difference in cost.  Particularly if the wet battery ever spills...

Note: it is becoming more difficult to find good quality wet
deep cycle batteries in the smaller sizes (U1 and 22NF).  With the
exception of the product of a specialty wheelchair battery company (MK
Batteries), the vast majority of wet "deep cycle" batteries I have seen in 
the past 2 years in these sizes have not been deep cycle but rather automotive.

I highly recommend MK Batteries  (click to open a window to their site-
this is the brand I sell) as they are the only battery company that I am aware
of that markets their batteries for use specifically in wheelchairs.
They have a staff that works with the wheelchair and scooter manufacturers.
Getting a MK battery means getting a wheelchair battery!


The size of the batteries is important.  Generally the manufacturer
specifies one size that is appropriate for that particular chair or
scooter- and that is the size that fits the battery box.  As the
battery size gets larger, the price goes up, so some customers (and
dealers) are inclined to put a smaller battery in to save $$$.  This
usually should not be done.  The larger battery will have slightly
more electrical output, and greater range before becoming so
discharged that it ceases to work.  Generally, the lower price paid
for the smaller battery is not compensated for in the life of the
battery.  It is cheaper to get the correct size because it will last
longer before having to be replaced (and may save the electronics from
failing due to low output).


  • Sealed Lead Acid Sealed lead acid batteries if properly installed should require no maintenance. Never remove the caps, or try to add water. No corrosion should ever be present unless the battery is beyond its service life. While the connections should remain tight for the service life of the battery, do check them and all other connections from time to time to make sure they are tight and in good condition.
  • Wet Make sure the connections and battery case are clean, tight, and free of any corrosion. Make sure that all connections are dry and tight- not just on the batteries, but everywhere on the chair/scooter. Due to corrosion, connections will loosen and connectors will deteriorate. Check the water on wet batteries every couple of months. Any water above the metal plates is "bonus". Don't go crazy topping off. This leads to over filling. As long as the plates are covered, and when you check the top of the plates aren't "dry", you are fine. An automatic charger should automatically shut off so that the only water loss is due to evaporation. If you are using a "clock" type charger, it may be necessary to check the water level more often and to adjust the amount of time every day that the batteries are charged. Check and add the water when the battery is "warm" from just being charged (ie: first thing in the AM if the battery was charged that night). That way it won't be overflowing by the water expanding when the battery warms up during its charge (normal). If the batteries are "drinking water like crazy" (and not filling over into the battery box) it means that they are "used up" and must be replaced. Failure to do so will not just strand you someplace, the gases escaping will corrode everything they touch and possibly cause an explosion which means: Do not smoke while checking the water in the batteries. Do not use a match or lighter for light to see the water level. Distilled water is preferred in areas with high concentration of iron or other minerals in the water. CHARGING (all battery types) Batteries should be charged every night if the chair is used for any distance that day. Some people find it more convenient to only charge a couple of times a week. This will not damage good quality batteries, but the user does run the risk of "running out" of power- particularly as the batteries age as their "range'" decreases. Unlike batteries in some cellular phones or camcorders, wheelchair batteries will not take a "memory" by charging before the batteries "run down". This should not be a consideration when deciding how often to charge. The best rule: "If you drive it that day, charge it that night". Another reason to charge daily is that it gives the user a greater safety margin if for any reason the chair or scooter cannot be charged. Example: power failure or charger failure. By always having "full" batteries, this buys you extra days when the batteries cannot be full (like always driving your car with a full tank of gasoline). Generally an overnight charge will be all you will need. I advise against leaving any charger on more than 24 hours, and while I would not go rushing home from the store if its been that long, I would make a phone call to have it disconnected if you are away from the chair for an extended period of time. If the charger is not shutting off (reading "full") after 12 hours, chances are the battery is beyond its normal service life and should be replaced. Or the charger is defective. BATTERY CHARGERS:
  • Never ever use an "automotive" charger on a sealed lead acid battery.
  • Remember, many (most?) chargers are 24 volt "out". Any kind of battery will be damaged and/or will damage the charger if the wrong battery/charger "combination" is used. And many chargers have the same size/style chair "plug", but are wired differently.
  • Never use a charger that was not provided with your chair/scooter unless a technician determines that it truly is computable.
  • Just because a charger is automatic, doesn't make it OK for Sealed Lead Acid batteries (gels). The "finishing voltage" is higher in a wet battery, particularly if the amperage of the charger is over 5 amps. It is that finishing voltage that kills a gel battery- sometimes in just 5 "cycles" and a gel mode's finishing voltage is lower.
  • I have found that gel-only chargers do just fine with wet batteries, but they take longer to recharge as they are 3 or 5 amps (instead of 8 or 10). A "dual mode" charger has the best of both worlds: high amperage and the correct finishing voltage. They are quite expensive, though. Lately, a new breed of "smart" chargers has come along. Some of these are quite reasonably priced (compared to dual-mode), and while most don't have the high output of the dual-mode chargers, they are so efficient that they charge even larger batteries quite quickly (still hours, though).
  • Never, never, never use a charger that does not have some method of shutting off, either automatically or through a timer. Some automatic chargers go into a "maintenance" or "idle" mode when the batteries are fully charged. These chargers are fine, but my "24 hour" rule (battery charging and care section) is even more important with them. STORING BATTERIES Batteries should be fully charged before storing, they should be stored in a cool, dry place. It is not necessary to take them off the chair, and certainly not necessarily to put them on a board rather than a concrete floor (modern batteries are in plastic not rubber cases and will not "short" to the floor). A battery will lose up to 1% of its charge every day, so after 3 months they will be discharged. For people who go away for a season (in Florida we call them "snowbirds") without their scooters/chairs, it is a good idea to have someone come in once a month or so to recharge (over night) the batteries. DO NOT leave a charger on the batteries (or plugged into the chair) for extended periods of time. Some charger manufacturers say that you can, but my experience is that if the charger malfunctions, you will have battery replacement (or worse) problems upon your return. I advise against leaving =any= charger on more than 24 hours, and while I would not go rushing home from the store if its been that long, I would make a phone call to have it disconnected if you are traveling... Keep in mind that the batteries are still ageing (albeit at a slower rate) when they are not used- the acid is still contacting the plates. And DO NOT remove (pour) the acid from wet batteries under any circumstances. BATTERY "FAQ's": Q: Will it hurt to drive my scooter/power chair several miles every day and then recharge every night? How long will they last. My car's battery lasts over 3 years A: If you have deep cycle wheelchair batteries, discharging them every day does not hurt. That is what deep cycle means: discharging and recharging once is a "cycle", and deep cycle means discharging so that the output voltage of the battery is under 12 volts (a fully charged "12 volt" battery will be around 14 volts on the charger when it is "finishing" the charge). Most batteries are good for a year, then replacement depends on how far you drive. After a year, the "range" of the battery and it's ability to "hold" a charge diminishes. Now I know that a car battery costs less and lasts for 3 (or more) years. I will tell you why that "rule" doesn't apply to a wheelchair battery: Your car battery is fully charged when you turn the key. It works for about 30 seconds, maybe up to 2 minutes, and then the engine starts. The charging system built into the car immediately recharges the battery and the battery becomes fully charged for the next "cycle". This is not deep cycling like a wheelchair or scooter. The only time that battery is used is when you turn the key or if you are stopped at a light with a lot of electrical accessories running- then the battery may "help out" the charging system for a minute or so until the light turns and you start to drive. Again, the "cycle" is not "deep". Now if you drive your wheelchair or scooter for 5 minutes and then recharge it, your batteries can last 3 years too. And you can use automotive "K-mart batteries" instead of expensive wheelchair batteries. When do you replace your batteries? When you don't have the "range" in one day (between charges) to take you where you intend to go. Use your fuel gauge and your "feel" of the chair to tell you when the batteries are getting sluggish, and ask if you drove a greater than average distance that day. If your answer is that you think the scooter/chair won't get you home, then it's time to change. Remember that if it takes X hours to get that fuel gauge to get to the half way point, it will be substantially less than X hours to get to empty because batteries are not fuel tanks and electricity is not a fluid. But if you travel your "circuit" every day without feeling the scooter (wheelchair) getting "slow", and you recharge every night, then it's not time to replace. If you know that the batteries are old, and that you will be giving the scooter/chair a major workout in a couple of weeks (vacation, etc), it may be prudent to change the batteries before the trip. Q: How do I maintain my batteries properly? Why does mine drink so much water? If I purchase Gel batteries, why does my dealer tell me I will need a different charger? A: When a battery is nearing the end of it's life (actually when it is beyond the end), it will start to use quite a bit of water. If it is more than a year old, replace it when it drinks water like mad. When you add/check water, do it in the AM while the batteries are still warm from the charge the night before. This is because the batteries will get warm enough to expand water out of the vent holes if a bit too much water is put in the night before the charge when the battery is cold. If you constantly are adding water, and the battery box is getting filled with water, you may be over filling (even if you are adding water when the battery is warm). Batteries will get warm enough in a "normal" charge to feel like a cup of warm coffee if you feel the battery case itself (not box). That is normal. Hotter than that may indicate a bad battery. This applies to wet and gel batteries. You will need a charger that has a finishing voltage of 28.4 volts or less (for a 24 volt system) to charge 2 gel batteries. Using a charger designed for wet batteries will burn out the gel batteries within a few charges as they will get so warm that the water inside (there is liquid in a gel battery) will expand and leave the battery (through one way vents) as steam. The battery will "bulge out" when warm, then "implode" inwards when it cools. If you see a battery (not the box the battery sits inside of) with sides that point significantly inward, that is why. Q: I have a scooter with the two Gel Batteries. How do you tell when the batteries are beginning to deteriorate to the point where they should be replaced? Do they just hold the charge less time or does the speed go down?. I have had mine over two years now and only use it outside the home to go to Drs appointments, shopping, eating out and visiting craft shows etc. Some weeks it is used a lot and some week at all. A: Both symptoms (less power/speed and less range) are symptoms of the end of the battery life. The third symptom is age: 2 years is twice what I tell my customers to expect from gel batteries (ie: one year life span). Even if the scooter is not used, the batteries deteriorate somewhat (after all, it's metal inside of acid). If you charge the scooter every night (or every time you use it), and can't go that day, then it's time to change batteries. And if you "put it off", you will be stranded. Avoid the "bargain" batteries advertised in some magazines. We have had more than one customer come in with defective one month old "bargain" batteries. For those customers, they turned out not to be such a "bargain". Q: How often should you recharge your batteries? I have only been doing it when I notice the indicator is getting low. Should I be recharging on a daily or weekly basis? Since we have a van with a lift and I don't expect to be doing much air travel the wheelchair "wet" cycle batteries may be a more economical replacement , not only as to cost but longevity. I have a separate charger for the gel batteries. Will I have to purchase a new charger or will this one work? A: The instructions I give to my customers is: "If you drive the scooter today, charge it tonight". Unlike some other types of batteries found in Camcorders and portable phones, no wheelchair battery takes a "memory" by charging it before it is fully discharged. Assuming your charger is operating properly, it will not shorten the battery life- and if the battery is of questionable quality", it may even lengthen its life by preventing true "deep cycle" that will ruin an automotive type of battery. Gel chargers work just fine in wet batteries. We have been keeping data on wet batteries charged on gel-only chargers for the past 8 years and have found absolutely no problem or shortening of life of the wet battery- providing the water is checked and added when necessary. Ironically, an improperly adjusted gel charger will burn out a gel battery, but when used on a wet, it only causes slightly greater water use- and if the water is added, the battery is not damaged. Check water (on wet batteries) every 3 months, more often if the battery was "dry" (upon checking), less often if it needed no water. After its 1st year, check every 2 months. When the battery starts "drinking" water rapidly, the battery is nearing the end of its life and will have to be replaced. Q: I am in the process of purchasing batteries from a magazine. Someone told me that if I install the batteries backwards they may explode. What did they mean, and will I know which end goes forward when I get them? A: The batteries don't load like a flashlight, with one "end" going into a container. They have 2 terminals that require cables to be attached. One terminal is marked positive, and the other negative. If you have 2 batteries, the installation procedure varies depending on the type/model of power chair/scooter. The problem is that the color of the wire going to the battery may not always "help" you in deciding how to hook it up, and any labels that may (or may not) have been installed at the factory may have deteriorated or disappeared. While red is usually positive, and black negative, on some Amigos, and most English made equipment, black is positive, white negative. On some equipment the positive terminal on one battery is connected to the negative of the other (putting the 2 batteries in series). That is where one potential for an explosion comes in (if your batteries are NOT to be hooked up that way or if both wires are accidentally attached in that manner). Another potential for explosion is when the batteries are wired correctly, but place in such a matter that if something metal gets in the box, it shorts the terminals (this happens more often than you may realize- particularly in older E&J and some newer Quickie chairs). Battery placement (relative to each other) and plastic covers over the terminals (originally provided by some manufacturers) prevent this from happening. If you don't know what you are doing, have someone who positively does install the batteries. This will prevent damage to you, the chair/scooter, and the batteries. This advice applies to all aspects of all wheelchairs and scooters. Learn the correct procedures before doing the work, or leave it up to a trained professional. Q: I thought that what I would receive mail order when I ordered batteries was what is currently on my scooter: a black box with handles and with plugs built into it. That's not what came. A: That battery and plug assembly is the battery CASE. Unless the company supplying the battery is charging you extra for the case (which can be very expensive), the battery shipped will not include the case. The case is there to protect the battery and to make it easier (in the case of scooters) to remove the batteries for loading the scooter into the car. The battery fits inside the case and the case does not/should not be replaced unless it gets damaged. All the information provided herein is Copyright 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, and 2001 Stuart L. Portner. All rights reserved. May be printed and reproduced for individual use, but may not be distributed without the permission of the author.
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