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John Williamson

Fast Charge your power wheelchair (powerchair) or scooter or any other deep cycle & starter batteries.

Detailed PowerChair Only Menu  |  More Charging Methods

My Latest BM3 15 MPH LITHIUM Powered Powerchair!

Contrary to what you may be told on other websites and by some manufacturers, it is perfectly OK to fast charge your powerchair or scooter with a much "bigger" charger (more Amps) than the slow overnight 5 or 8 amp charger that it came with. With a few IMPORTANT considerations:

  • Never try to put more Amps (with a bigger charger) into your batteries via the powerchair or scooters normal "charging Socket".   You may well damage it, or the wiring or even the control system. Instead, fit an additional plug and socket wired directly to the batteries. This is a simple thing to do. (See powerchair image below) If you don't know how to do this then either give up now or find someone that understands basic auto electrics to do it for you This is important or you will probably fry something!

  • Its perfectly safe to fast charge most lead based batteries without any "Amp" or current limit whatsoever. Technically this current (Amps) that the battery draws when connected to a big charger, or big fixed voltage power supply is called the natural "inrush current". Most battery manufacturers of quality batteries agree that there is no good reason for any limit.  And to do this safely it only needs to be a STABLE fixed correct voltage. Without any Amp limit imposed. Of course the charger or power supply will be the limiting factor. 

    When a battery is pretty well discharged down to say 12.2v after you have been shopping with the GF for example, then if you were to connect it to an imaginary "fixed" voltage supply of say 14.1 Volts for gel batteries (28.2V with a pair of batteries obviously)  the the current "rushes in" until the battery voltage rises up to match the 14.1 Volt supply per battery over time.  the Amps start very high and then fall away naturally as it becomes charged.

    That's exactly what your small wheelchair charger (to begin with) does. Or a cars alternator does (its permanently "fixed" at a set voltage while the engine runs)  Your wheelchairs small 5 or 8 Amp charger is "limited" unnecessarily (other than cost), to 5 or 8 Amps maximum. Your car alternator is limited to around 100 amps. Neither will hurt any 12v battery. The only affect is to charge much faster!

    When a discharged battery is connected to a fixed voltage supply, the current (Amps) that the battery draws ("pulls") which can be up to around 100+ Amps to begin with, slowly falls away until its typically A FRACTION of an amp as the batteries "charged voltage" almost matches that of the supply voltage. 

    At this point (when the current in Amps falls to a very low value) the battery is around 95 percent charged. And you could then happily disconnect it and go to the pub. I often do. This REALLY isn't harmful!. Its also exactly what your cars 100 Amp fixed voltage alternator does to your cars battery every time its started up! 

    So with a GOOD QUALITY AGM battery, such the Odyssey ones I use, that's about 40 minutes to go from say 60 percent discharged to 95 percent fully charged. About two to three times faster than a gel battery. Its Just NOT harmful to batteries in any way for the majority of 12v deep cycle wheelchair, or car starter batteries. In fact doing this regularly extends battery service life hugely.
It was thought for many years that this fast charging treatment was harmful to your batteries & will harm or shorten the life of your batteries. Problem is that now all the so called "experts" think they know that this is true!  But it really isn't! Its much like the story about Ni-Cad batteries developing a memory! Everyone KNOWS that its true. Well its just as wrong. They don't. They never did. At least the only time it ever happened was under a specific set of very hard to reproduce circumstances on a satellite by NASA in early days.  And even they had much trouble reproducing it. Its just a myth. The real reason for low charge rates on lead based batteries is because in the early days accurate voltage control, and fancy 3 stage charging profiles common to almost all new chargers today didn't exist. So charging at a slow speed minimised the problems caused by incorrect voltages.


Heat over 50 centigrade during charge can cause damage and is caused by high internal battery resistance (nasty cheap deep cycle batteries or an "old" used up battery) or by OVER CHARGING (too high voltage) a "recombinant" type battery such as most sealed power wheelchair batteries. But charging at a very high rate but at fixed safe voltage does NOT overcharge a battery and so is perfectly safe.

wheelchair / scooter charger

My own 30 amp powerchair charger. And some connecting leads.
6x faster charging than the original equipment 5 amp one!

Since quality deep cycle batteries with much lower internal resistance are now the norm (the main source of the heat at high charge rates) then this is no longer a valid reason not to fast charge them. The advantages to the user are huge, and battery longevity resulting from regular top up during the day is vastly improved. Due to the lower average depth of discharge.

Another source of heat in sealed batteries is the chemical recombination of hydrogen and oxygen caused by overcharging. (Too high voltage!) But since we now have very accurate logic controlled chargers this is no longer a valid reason not to fast charge them.  In the past charging a 70 Ah battery with say a 8 amp charger meant that even if the charger charged at too high a voltage no external gassing would occur since the recombination capability in sealed batteries would be able to re-absorb the gasses easily. So no external gassing would occur. In other words its far less critical to get the charge voltage right at a slow charge rate and so its "recommended" by many battery companies. They don't want batteries back under warranty!  So recommending low charge Amp rates is safer when a crappy charger is used!  But we don't have crappy chargers any longer!  Well I don't anyway... All switch mode multi stage chargers should be safe provided you select the correct type for the batteries you use.

Now, knowing that Some manufacturers actually suggest a "no current limit" and fast charging as a preferred charging method (such as some AGM batteries: Hawker Odyssey and Optima and many others) and no current limit may involve hundreds of amps, then you will soon see that using say a 25 or 30 amp logic controlled 3 stage charger on a powerchair with big 70Ah batteries is not only sensible, its actually really extremely cautious! And far from the hundred Amps plus that a cars alternator would charge them at.

If a PowerChair battery can produce hundreds or even thousands of amps as some quality AGM deep cycle batteries can, then charging them at 30 amps is actually a very conservative approach. After all charging is exactly the same reaction as discharging or starting a car. In reverse.  The only time that limiting the current while charging a Deep Cycle battery becomes important is if that battery has a high internal resistance as some cheap nasty ones do.

Does it harm them? No, Contrary to what ill informed wheelchair manufacturers may tell you it does just the opposite. Many studies on deep cycle battery powered machines such as airport floor cleaning machines, etc have shown that fast charging deep cycle batteries actually helps them live longer especially when used as regular opportunistic charge system. It appears to actually be very good for them.

The only thing that damages them is either over charging them (going above say 14.1v or 14.4 volts per battery for a typical battery (see your batteries spec sheet).  Or continually undercharging them. Undercharging, or really deep cycle use, heavy discharge, or not doing a complete charge often enough are the things that damage your expensive batteries.

Fast charging only replaces typically 95 percent of your charge due to something called acid stratification and plate surface charge. A reverse Peukert effect. You batteries STILL NEED an overnight charge and long soak with your slow charger as well. Every night if possible or at least every few days if that's not possible.

This keeps all of your two batteries cells equalised and properly balanced and sulphation free. Otherwise they can get out of step. Which is very important for battery longevity. Depending on the charger you use this fast charging will only replace about 90 to 95 percent of the capacity. in about an hour. Its intended to let you charge or top up in the middle of the day or before going out in the evening.

My wheelchair batteries are on charge here. This is a Clamp Ammeter. It started off when first connected reading 30 amps. It always does if the batteries are pretty much depleted.

When first plugged in the batteries "suck up" as much as the charger will let them. If its a 30 amp "capable" charger like this one is then it will deliver 30 amps in its first charge "stage" (of 4)

It is, like most modern chargers, a fixed regulated voltage (28.8v in this case for two AGM batteries) for as long as the battery sucks up the 30 amps that the charger is capable of delivering. If it was a 60 or 100 amp charger then that would be fine too. And it would then be able to raise the batteries voltage to 14.4 (28.8v for two) even faster!  And that's quite safe for the batteries. The current (amps) gradually tail off once the battery achieves the set 14.4 (28.8) volts...

In this case above the charger is 30 amps. So that's what the batteries greedily take. That's because the charger is basically a fixed voltage power supply with a current supply that is limited. Just like your standard 5 or 8 amp powerchair charger is limited to just 5 or 8 amps... 

Once the battery "achieves" the set voltage then the current starts to fall away from the maximum the charger can do, and that is the end of the so called "stage 1" and stage 2 begins. Nothing actually changes other than the current drops to keep the battery from exceeding the set FIXED voltage. So this continues until the current falls NATURALLY to a very low level. That signifies the end of "stage two" on your 3 or 4 stage charger.

The next stage is simply a permanent lower voltage "float" that goes on forever. This stops your battery from deteriorating over the long term. Stage 3 then never ends... In fact in a powerchair only two stages are really needed. And if you are unplugging it after the green "ready light" illuminates then you don't use the third float stage anyway. It happens AFTER the ready light.

I also have a 100 amp charger (a 12v one) and this charges single loose batteries quite safely too. As long as your batteries manufacturer specifies no inrush current limit then its not a problem no matter what other so called "experts" may tell you.   However, the faster you charge a lead acid battery the lower the amount of charge you actually put back. This is due to the acid having no time to level out its state of charge and the charge is mostly at the plate surface.. The "deeper" charge takes time to penetrate the battery plates. This is the reverse Peukert effect. 

The name for this is charge stratification. So a fast charge in a good quality low resistance battery may only really be 90 percent charged. So a slow charge at 1/10th the batteries capacity (your stock slow wheelchair charger) is recommended either every night or at least every few days to fully equalise all the cells and keep your batteries in balance and healthy.

I use both of these 30 and 100 amp chargers on all my batteries over the last few years without any problems whatsoever. In fact they now last longer due to the lower average discharge levels that a fast top up in the afternoon gives them. Ready to go out again and a green ready light (90 to 95 percent) usually well under an hour...

Clamp Meter showing a powerchair charging current After around 10 to 20 mins depending on discharge level it falls slowly (to 21 amps here), as the battery becomes charged up and it own voltage is closer to the supplied 14.4v (28.8v) voltage from the charger. This part where the battery no longer pulls the full 30 amps from the charger is the "second stage" of a two stage charger. And so far it didn't do anything apart from supply a fixed voltage and a maximum current of (in this case) 30 amps... So we get duped. A two stage charger is really that simple.

As charging nears completion and the battery voltage slowly rises less current naturally flows. The current keeps on falling.  When it reaches around half an amp in this case above (depending on rate of fall etc) and your battery is just sat at 14.4 volts and needing little power to hold it there the charger says done!  That's the end of the stage 2.

It then switches to "float" mode which is in this case is 13.4v per battery (26.8 volts.) measured. Ad it will hold your battery there for ever. Float charging isn't really "charging" at all. It just prevents the batteries natural internal discharge from happening. So its quite safe to leave connected for very long periods or just overnight. 

But you can go from pretty much discharged after shopping to 95 percent plus charged in under an hour ready to go out for the evening. Most normal 3 stage chargers are now finished whether fast chargers or slow. See? They are really pretty simple.

Not ALL batteries can be fast charged safely. But almost all can.  Almost all AGM type batteries are perfectly happy to be fast charged. Optima, and Hawker Odyssey for e.g. both actually recommend this for batteries used in a cyclic system such as a Powerchair or Scooter. See their spec sheets.

Hawker Odyssey actually supply and recommend a 50 amp charger to be used with all of their batteries from the tiny 8ah
one (no misprint - that's 5 times smaller than a typical powerchair battery!) upwards... Here is a link to a supplier.

Read the specs for their OMAX-50A-1B http://www.odysseybattery.com/chargers.html   They as a battery manufacturer don't consider it at all unusual to feed a tiny 8 amp hour PC310 battery (in the charger specs) A FULL 50 Amps to charge it.  The battery just naturally takes what it needs.  So charging a pair of big 65 or 75 Amp Hour wheelchair batteries at just 30 amps is barely tickling them!  

All that matters is that you don't charge above 14.1v each for GEL batteries or 14.4v for AGM batteries. And the charger takes care of that! So safely ignore what you may read on so called "professional" web sites about sticking to the charger that the manufacturer supplied!  IN FACT THE FACTORY SUPPLIED CHARGERS ARE OFTEN THE CAUSE OF EARLY BATTERY DEMISE.

Some Gel batteries are also quite happy to be charged at a fast rate without any problems.
The widely used MK and Sonnenschein deep cycle Gel batteries are also happy with this treatment. Although they take a little longer to charge (higher resistance and Mr Ohm make this happen!) See their own specs on acceptable charging before you try this. And read the part about the inrush current limit. They don't have a limit. I have been fast charging both of these brands after speaking to both companies and the MK rep in the UK. They seem to show no detrimental effects whatsoever and I now get longer battery longevity because of it due to the average depth of discharge being far less. As long as care is taken selecting a charger that keeps to or below their charge voltage limit.  See appropriate spec sheets for your chosen battery before proceeding or don't blame me!

My specific Powerchair Fast charging details:

30 Amp Anderson Charging Plug Power Wheelchair

Using THIS plug (Anderson plugs and sockets) fitted to my powerchair and connected directly to the battery terminals I fast charge my power wheelchair most days. Don't try this fast charging via your wheelchairs charge socket! It will melt something expensive!

Fitting Anderson connectors to your powerchair for fast charge and connecting other equipment

I use this 30 amp fast charger. 4 Stage logic controlled 30 amp switch mode efficient device.  I have 3 actually, one in my van just in case and one as a spare!  It can be used to charge up my powerchair (2x 70 ah batteries) to 95 percent+ fully charged in around 1.5 hour ready for an evening out!  That's if your batteries are pretty beat up. If you are only about a third or half discharged then its faster still to a green ready light!  See also Fast Charging Your Powerchair


Switch mode 30 amp, 1 hour fast charger.  Fully digitally controlled 4 stage safe fast charging. Designed for Good AGM batteries like the Optima and Hawker Odyssey ones that I use.  You do not need this specific charger ANY 24v HI AMP MULTI STAGE CHARGER FROM 10 TO 100 AMP WORKS GREAT. The bigger the better. (Faster)  Mine came from eBay as a caravan/leisure charger. It can also charge 12v, 24v, 36v, or 48v as well. About 100 UK Pounds. So I bought 3.

Full slow overnight charging with your standard 5 or 8 amp charger is still required at least every second day or so however (to equalise and "even up" all the cells properly and to prevent long term sulphation) but opportunity charging during the day, say 5PM while you check your email,  is both advantageous to the user (its invaluable since you go out again "topped up" and ready for anything the world may throw at you) and it makes your batteries last longer due to a lower average depth of discharge.

Charging the batteries at 30 amps (or much higher) opportunistically as often as you get chance is perfectly within the batteries specifications and capability AND helps them live a longer life..

I use this charger above although there are plenty to choose from. Google and eBay (sometimes) are your friends! http://www.batterychargers.com.au/sa-mbc-multi-voltage-lead-acid-charger.html

list of bigger faster chargers RECOMMENDED and sold by the hawker battery manufacturer. http://www.odysseybattery.com/chargers.html

Soneil multi stage switch mode chargers - find a dealer! All will work and be safe with AGM or Gel batteries the 30 amp one is the most suitable for 70ah batteries and maybe 20 amp for 40ah batteries. 12 amp for small 25 or 30ah batteries.
2424SR - 12 amp
2430SR - 15 amp
2440SR - 20 amp
2450SR - 25 amp
2460SR - 30 amp

http://www.soneil.com/24_volt_high.html  All are on this page.

The internet is full of suitable chargers like this Gel and AGM safe one http://www.batterystuff.com/battery-chargers/24-volt/gel-cell/SEC24-25.html

Or for AGM only batteries http://www.batterystuff.com/battery-chargers/brands/iota/IOTA-DLS2725.html (slightly higher voltage for faster charge rate to suite AGM chemistry.  Personally I find eBay easier.

Or 24v and 25 amp charger http://cpc.farnell.com/1/1/40250-charger-24v-25a-lead-acid-ac2524-ideal-power.html

12 amp one here that does 12v or 24v http://www.mynewcheap.co.uk/products/details/sterling-pro-budget-12a-24v-charger/14159/

This one is especially interesting as it is actually two isolated 12v chargers built into one case that are completely electrically isolated. Available as 8 amp or 20 amp power outputs. So you can charge both your 12v batteries in your powerchair at once but separately. Rather than in a series "string" configuration. This has the advantage that its never possible to have one battery in a higher state of charge than the other. Both your batteries will always be charged to exactly the correct level which has many benefits over the stock charge method.   http://www.marcleleisure.co.uk/store/prosport-water-proof-battery-charger-amps-p-251.html?cPath=24_47   You will need to fit TWO charge connectors to your chair though. Fitting Anderson connectors to your powerchair for fast charge and connecting other equipment

Expensive and similar to the above in that it charges your batteries individually (which is superior) and can do three at once! I plan on adding an extra battery so that I can use 36v instead of 24 in the future with a different control system.


Personally I have started looking at Lithium Phosphate batteries. These can also be fast charged, are about 4x better at energy storage and cannot explode like Lithium Ion or Lithium Polymer batteries.  Imagine the speed or range that that will allow! And the weight saving. They are expensive, but they can do 1500 80 percent discharge cycles compared to 400 to 500 of GOOD lead acid batteries... WHY ARE THE MANUFACTURERS NOT ALREADY USING THESE THINGS? I know they will have hundreds of excuses but the real reason is they don't care and cannot be bothered to learn what's possible and do any development work.

Lithium Ion Batteries for Powerchairs and Scooters



Related Pages

Charge a Powerchair directly from a vehicle. via the same Anderson connectors

Anderson Style connectors and why you need them

Fast Charge YOUR Powerchair in Around 1 Hour

Inverters & Chargers

Batteries for Both Vans & Power Wheelchairs

Which Batteries to Buy

Very Flexible Charger!


Lithium Ion Batteries for Powerchairs and Scooters

My Power Wheelchair or Scooter Will Not Charge

BCI Battery Sizes, Group 22, 24, 34, 27 etc

Drive Your Powerchair by Radio Control

A Superior Powerchair overnight charger

Battery Planning How to organise yourself for every eventuality!

Powerchair Battery State of Charge


MORE: Detailed PowerChair Only Menu


Hyperion ChargerHyperion charger can charge almost any battery. Including your wheelchair from your car or the other way around!



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