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John Williamson

Charging power wheelchair & vehicle batteries

Related:  Inverters & chargers  &  About powerchair & vehicle batteries & Which batteries to buy & More charging methods

1. Charging your car / van battery:

Maintainance-chargerIf your accessible vehicle is driven daily then there is no need to charge it. The vehicles own electrics will do it for you.  Unless you left it sat unused for too long or you left something turned on!

The cars alternator charges it at 14.4v (or close) as soon as you start it up and charges the battery fast at around typically 100 amps at a fixed 14.4 voltage. This is ideal for a starter battery. The danger is if its left unused for say a week or longer.

All modern cars have such things as immobilisers, remote locking, engine management computers, alarms, various radio memory and other electronics that drain the battery as the car just sits there.

In some cases pretty quickly over a week or so.  With extra electronics such as remote start, or say the computer in the boot of my wheelchair adapted minivan that controls the ramp, electric doors, suspension lowering and more the battery has double the drain on it while I get out and then again whilst it is sat unused on my drive! 

This damages ordinary car starter batteries quite fast through sulphation even if there is enough energy left to start the engine most of the time. So you will not necessarily know anything is wrong. Your battery will just suffer an early expiry.   See All about powerchair & vehicle batteries for more info.

Every time you switch off and get out, the ramp and suspension lowering (on my car for E.G.) as well as the door opening and closing motors all use lots of power. Your battery is already in a slightly discharged condition after you just exit it after a long drive. Batteries store or age well in a fully charged state. But they all sulphate internally if left in even a slightly discharged state for very long. In a relatively short time the batteries capacity or starting capability is then reduced.

Compounded by the fact that all those electrical systems mentioned above are still gradually taking even more power out, over time, as it sits there on your driveway. 

So if you leave your car or van for more than a week its a good idea to charge it. Or more accurately to "maintain" it in a healthy fully charged state. Your battery will stay healthy longer.

Buy a battery optimiser or battery maintainer as soon as possible if this scenario sounds like you!

Your battery will love you and it will stay healthy much longer. It doesn't actually need a full charge (although that wont hurt) but it needs a maintenance charger like this Optimate at the top of the page (or something similar) connecting and leaving connected while you are not regularly using your car.

It may well still start if you don't bother but your battery is suffering and will, sooner or later, let you down. Another alternative is a good solar charger of 2 to 5 watts. It wont "charge" your battery but it will keep it topped up hopefully and prevent it going flat and sulphating. Less than 2 watts is a complete waste of time unless you live in Arizona!  I leave a 5 watt one above plugged into the cigarette lighter socket and sat on my dashboard when I am not using my van. It keeps my battery fully charged up and healthy if the vehicle is unused for long periods. of a week or more!

Measuring battery voltage

See larger image of the Hawker Odyssey battery under test. 

Here is an example:

My Disabled adapted Rollx van. Has all kinds of immobilisers, satellite navigation, engine management, alarm and an extra computer in the boot to control the ramp/door/lowering etc.  Here it is with the vehicle all locked up and the engine stopped. After 30 mins. The Clamp Ammeter shows a 0.2 amp (200m/amp) drain on the battery. This is quite high but similar figures may be typical for some other modified vehicles of this kind.  20 to 50 m/amp is more normal.

It initially starts as 10 amps plus after switching off getting out and locking the van!  10 Amps!  But gradually all the various electronics go to "sleep" and it settles at this relatively low value. The voltmeter shows the brand new Hawker Odyssey battery is fully charged at 12.8v.  Now 200ma at 12v is 2.4 watts. Or about 0.2 amps lost per hour while parked or 4.8 amps per day. This looks abnormally high but it always seems to settle at that figure. 50ma is probably closer for most vehicles.

That means that in ten days time if I don't drive it or charge it the battery will be 2/3rds drained!  that's right 2/3rds!!! It will have suffered some sulphation and had its service life shortened. It will also probably still start the Van - Just!  After two weeks? Doubtful if it would.

Now you see why I use Optima or Hawker Odyssey batteries? They are both dual purpose Deep Cycle and Starting Batteries. This way the slowly discharging battery is much less damaged than an ordinary starter battery would be.  Most modern vehicles are like this. Have yours tested.  A deep Cycle and Starter battery is often a much better option in most modern vehicles, including standard non adapted ones.


You may like to consider fitting a dual purpose STARTER & DEEP CYCLE battery to a mobility vehicle if it has extra equipment like a powered ramp or wheelchair lift etc.

Because these are a special "breed" of battery that can both start a car as well as being Deep Cycled like a powerchair or scooter battery.

So that all those times when the battery gets a bit low due to the extra drain after the engine is stopped will do much less damage to your battery. Examples of these include the Optima, Hawker Odyssey. and a few others. 

Not cheap but being disabled seldom is. And we need the security of a good battery more than anyone else.

See All about powerchair and vehicle batteries



2. Charging a powerchair or scooter battery:

Powerchairs and Scooters use Deep Cycle Batteries. These, despite their name, DO NOT LIKE  BEING DISCHARGED! All lead based batteries hate it, but deep cycle batteries suffer less damage when doing so.

With this in mind its best to ALWAYS charge them fully every single night in a powerchair or scooter if used at all during the day.  And once a week even if NOT used at all.  With the manufacturers charger or something equivalent with the correct charging profile for whatever batteries you have fitted.

A good Deep Cycle 3 or 4 stage logic controlled charger (switch mode or transformer) designed for the type of battery that you use is essential. Even if you only used your Power Chair or Scooter for ten minutes you must do a complete charge every night. Don't Forget. If you do and you continue to use it you will discharge your batteries much deeper than needed and no lead based batteries really like that. Regardless of what any "expert" may tell you!

REMEMBER!!! Charge weekly if you don't use it.   Nightly if you do use it.   Overnight.

If you have not used your powerchair or scooter at all then charge it once every week. Fully over night. Once a week will help prevent the batteries becoming slightly discharged and internally sulphated which ultimately is what kills them, if just left and allowed to become discharged. Never discharge Lead Acid Deep Cycle batteries on purpose to get rid of any memory effect!  They don't have a memory!  Even the original rumour that Ni-Cad batteries had a "memory" that came from NASA was not actually true in any normal use. All deep discharge does is damage your wheelchairs batteries faster.

If you get chance during the day it IS BENEFICIAL to plug in the charger to lower the average daily discharge level. This is called opportunity charging. Or opportunistic charging. Contrary to what you may read elsewhere by the less well informed it is definitely beneficial.  Anything that lowers the average discharge level each day helps your batteries live longer. It still needs the full overnight charge however every night just the same. The FULL charge cycle doesn't just "charge" but it also equalises all the cells in each battery bringing them all up to the same voltage level. So Plug it in for a while if you get chance while sat at a computer for watching TV.  But also do the full overnight charge too. Opportunistic charging does NOT replace it.

Are you fed up with waiting hours for your chair or scooter to charge? Well depending on your battery type you CAN fast charge them. I use Optima Deep Cycle and Starting batteries (Yellow Top ones) or Hawker Odyssey AGM batteries partly because it allows me to charge them up in the middle of the day up to a 95 percent full charge in around one hour. Go from all but exhausted, to ready to go again while you check your email... See here.  

It still needs the full overnight charge while you sleep from the normal slow 8 amp (or about 20 percent of battery capacity) charger however every night just the same or your batteries never get properly equalised and will become unbalanced.

Contrary to what you are told on certain other websites fast charging or opportunity charging your deep cycle batteries isn't harmful and can lower the average depth of discharge meaning longer service life. But you do need to connect directly to the batteries and not try to put extra current through the normal charging socket... See here

Normal overnight (slow) charger size?  Its NOT at all critical unlike what some so called experts would tell you. The sizes below will get your heavily used scooter or powerchair fully charged and ready to go while you sleep. Smaller wont hurt the batteries at all. Even a 1 amp multi stage charger will safely charge your batteries. But it will take way too long!

3 amp for 25 amp hour batteries.
5 amp for 35 to 45 amp hour batteries.
7 to 8 amp for batteries 50 to 75 amp hour.

If you try to charge with a bigger charger but still of the correct multi stage deep cycle type then several things can happen.

(a) Depending on battery type you may have no problem at all. Your batteries will just charge faster. These chargers are voltage controlled so even a big charger will not hurt a good deep cycle battery unless it gets too hot. Too hot means about 50 degrees centigrade. I charge mine regularly at 30 amps.

My batteries (Optima) show no sign of stress and the manufacturers suggest that there is no limit to the current at all. Not only is my 30 amp charger OK its fine to use a 200 amp one.   However charging faster MAY shorten battery life if they get hot (50+ centigrade). But even at a 100 amp rate they only get vaguely luke warm so its just not a problem.

b) If your batteries are less good quality you may find acid or gelled acid all over the place! Check the manufacturers website for fast charge current limits. Optima's for e.g. say no problem at all...

Hawker, (+ Sonnenschein I think too) also say its not a problem other than watch the temperature. And after talking to the MK guys they also say no inrush current limit is applicable.

So its safe to fast charge all of my batteries at least! And probably all the others too.

c) don't ever put more than the standard chargers output (5 or 8 amps) through the stock charging socket! Connect your own cables and connector directly to the batteries


Some Related Pages on this site: 


Much more:


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Very flexible and useful Hyperion charger can charge any battery. Including your wheelchair from your car or the other way around!






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