Does charging your car battery on fast charge damage it?

[Simon Robinson 4Participant @simonrobinson4]

Ive got two settings on my car battery charger. High and Low. I’ve heard that using the high charge often can distort the electrodes over time. But surely when I drive along the motorway the battery is getting a much higher charge from my alternator than any plug in battery charger can even give it.

Any thoughts?

[Simon Robinson 4Participant @simonrobinson4]

[Ady1Participant @ady1]

A healthy battery should be fine

[Pete RimmerParticipant @peterimmer30576]

Just another 'common myth' that makes sense until you think about it properly. A 15amp charger isn't going to distort plates that deliver 120amps to the starter.

Fast charging might warm the battery up and cause the electrolyte level to drop over a long period.

Edited By Pete Rimmer on 23/11/2021 14:37:34

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Simon, I don't know the answer, but I don't think you can compare the two. The charging circuit in your car is probably controlled more precisely than your plug in one and of course the car's electrics will also be drawing current and the circuit will also be controlled to keep levels in order and balance between the battery and the car's demand.

Regards Nick.

[Clive HartlandParticipant @clivehartland94829]

The principle of a lead acid battery that I was taught was that it will take what it needs to re-charge.

A battery low in charge will draw a deep current and as it starts to reach full charge it tapers off.

Beware overcharging, so take note of the time and check regularly on it's condition.

[IanTParticipant @iant]

I will just mention that newer (Start Stop) batteries do not like old battery chargers (don't ask how I know!)

I now have a new 'Start Stop' charger (from Halfords) that offers 'fast' & 'trickle charge' settings which seem to be fine. It was much cheaper than the new battery.

The old battery charger is now regulaled to rust removal (electrolysis) duties – for which it is ideal.

Regards,

IanT

[JuddyParticipant @juddy]

I think the tale of high charge rates damaging batteries comes from when dealerships would stick an 100amp charger on a battery prior to a test drive, or leave the a high amp charger on for extended periods of time which will distort the plates heating the battery drying out the fluid. Years ago buying a second hand car from a back street dealer normally resulted in the car needing a new battery fairly quickly after purchase. Probably not such an issue nowadays with regulated & controlled charging from modern chargers.

[SillyOldDufferModerator @sillyoldduffer]

Is the battery charger being used a lot? If so, it suggests something is wrong – too many short journeys, failing battery, capacity too small for the vehicle, stuck boot-light switch etc. A healthy battery in ordinary service should recharge on the accumulator. (Assuming a modern car. They seem kinder to batteries than older models. I think because electronic voltage regulators are more sensitive and react faster than mechanical types. )

Distorting plates isn't the only way of damaging a battery. Overcharging takes years off them! Cheap chargers ignore all the warning signs if a battery is put on fast charge and allowed to carry on past full charge. Better units back-off automatically, so much depends on the electronics inside. My classic charger contains a simple transformer and rectifier and has to be supervised.

Jump start rechargers are another ball-game. The usual size might max about 1250A into a battery, which could cause bent plates if done too often. Conversely, shaking up Sulphated plates can revive a failing battery, though the recovery is temporary, not a permanent cure. Needing frequent jump-starts suggests something is wrong too.

Dave

[Ex contributorParticipant @mgnbuk]

Ive got two settings on my car battery charger. High and Low.

The rating plate on the charger should say what the charge currents are for both settings. I would guess at Low being 1-2 amps & High between 4 and 8 amps, depending on how expensive the unit was. Rule-of-thumb for charging a lead-acid battery I was taught was to charge at around 10% of the battery capacity to prevent damage, so 10A for a 100A battery. If your car has a small battery (say 45 A) & your charger is 8 A rated you may be a bit on the high side, so if you have the time charging it for longer on low may be beneficial.

In the car the alternator will be supplying all the vehicle demands + just replacing the amount taken from the battery by starting the engine – the full output of the alternator isn't going through the battery.

Nigel B.

[Simon Robinson 4Participant @simonrobinson4]

Posted by IanT on 23/11/2021 14:54:21:

I will just mention that newer (Start Stop) batteries do not like old battery chargers (don't ask how I know!)

I now have a new 'Start Stop' charger (from Halfords) that offers 'fast' & 'trickle charge' settings which seem to be fine. It was much cheaper than the new battery.

The old battery charger is now regulaled to rust removal (electrolysis) duties – for which it is ideal.

Regards,

IanT

That’s sounds a good idea. Never thought a car battery charger could be used for electrolysis. So I guess you put the negative clip on your work and the positive on something else or the other way around?

Thanks

[SamsarandaParticipant @samsaranda]

IanT can you elaborate on what your old battery charger did to your start/stop battery? I have a start/stop battery and during lockdowns have not been using the car very often consequently the battery has needed charging at various times, I don’t do much mileage. The battery is about five years old and probably reaching end of reliable life, I have a battery charger which I bought at the start of first lockdown, it has two charging rates and I only use the low rate charge. I am very interested to know what damage a conventional battery charger could do? Dave W

[IanTParticipant @iant]

Yes – I was doing very little mileage during lockdown and my 5 year old car wouldn't always start after a week or so on the drive. Tried re-charging but it increasingly didn't seem to work. Investigated and found out I was probably accelerating it's demise. This link explains the problem…

Can I use any battery charger?

Regards,

 

IanT

 

Edited By IanT on 23/11/2021 17:13:17

[J HancockParticipant @jhancock95746]

A 'standard ' cheapish battery charger output is not really 'dc' like the battery output , so be careful what you connect it to if not a battery .

[john fletcher 1Participant @johnfletcher1]

Simon above, make the sacrificial ANODE the POSITIVE and the object to be de rusted Negative. I use diluted washing soda in a plastic bucket and wear some disposable gloves. You will be amazed how well it cleans things the first time you do it. Lots of scum and of course if you don't clean up the object further and protect it, it soon run again. John

[BazyleParticipant @bazyle]

In an old charger the 'fast' or 'high' is an unsmoothed full wave rectifier. The 'low' setting is just turning off half the diodes so it is an half wave rectifier. Each pulse of current is the same as before just half the time it is completely off. Also part of the cycle is below the 12v so not charging then anyway. Finally do you really think they put enough copper in that cheap charger's windings to put out any heavy current.

[Ady1Participant @ady1]

Overcharging is the only caveat

The old chargers needed to be turned off manually or they "cooked" the battery

[Howard LewisParticipant @howardlewis46836]

Modern lead acid batteries are much improved over those available many years ago In those days, a 2 year guarantee on a new battery just about stated it s expected life.

In those days a Lucas C40 dynamo could deliver 22 Amps maximum. Modern Alternators can deliver 100, and the charging control systems are much more sophisticated.

My first car, a Singer 9, had three charging rates; determined by the resistance between the battery and the field windings of the dynamo, depending upon the lighting load..

My last car still had the original battery in good condition, (judged by the green charge indicator ) when it was sold after 12 years!

The thing that is most damaging to a lead acid battery is to leave it discharged. That accelerates sulphation of the plates.

Howard

[Bill DawesParticipant @billdawes]

Happy memories of my first car, a 1946 Austin 8. I think I ran it for years with a dead battery, started with a handle and then probably just ran off the generator, driving along country lanes at night was especially exciting, slowing down for bends caused the engine to die, clutch quickly in, lights off, bump start, first gear to keep revs up, lights back on just in time to negotiate bend.

A bit of 'expert' tuning of the regulator to increase charging the next day kept me going for a little longer.

Bill D.

[Ian MellorsParticipant @ianmellors72388]

Not really answering the question, but my car (a WRX Impreza) does 10 mins to work and back so it is plugged into an Optimate trickle charger over the weekend. It was also so connected during lockdown last year and during my enforced stay in hospital over this summer.

Can't recommend such a device enough. Will do it's best to resurrect a deep discharged battery too

[SamsarandaParticipant @samsaranda]

My first car was a 1954 Ford Popular with the 1172 cc side valve engine, the electrics were 6 volt and the headlights were dire at the best of times. Was glad of the starting handle on many occasions when it was cold and frosty and the battery was sluggish to respond. Because it was 6 volt electrics it lacked electric windscreen wipers, it had vacuum operated wipers, you didn’t put your foot down in heavy rain because the wipers would stop dead no vacuums to run them. For all its faults I loved that old car, when I was overseas the wife sold it to her brother and he blew the engine up on it, I still haven’t forgiven him for that and that was 1967. Dave W

[john fletcher 1Participant @johnfletcher1]

Dave W should you ever get that ford POP back, I'll forward you details of how to over come those Vacuum operated wind screen wipers and to fix advance/ retard to the distributer as well. I had a 1934 Austin 7 with the same problems and with 3rd brush dynamo. I can't remember, details of the POP dynamo or charging arrangement, I should, as wife's brother had one. I remember we changed the cylinder head from another Ford engine which raised the compression ratio and it then was quite a flier. Side valve engine of course, how crude was the valve adjustment. John

[Tim StevensParticipant @timstevens64731]

Batteries do not respond well to high current on charge. But of course, we don't know how high the high setting is in practice, and we don't know the size of the battery (in Amp-Hours). My answer would be: Get yourself a modest ammeter reading up to 10 Amps, and measure the current going into the battery on High, and on Low, charge settings.

A normal car battery of about 50 Ah can be charged at 8 to 10 Amps – as long as you turn it off when the process changes to 'gassing' – with lots of bubbles and gurgling – which means that all the chargeable stuff is now fully charged. Much more than that – either more amps or more time – will tend to overheat the battery – it should never get hot enough to feel more than warm. This causes damage to the chemicals and reduces the available charge.

Hope this helps

Cheers, Tim

[noel shelleyParticipant @noelshelley55608]

Chargers of more than 10 amps are not so common now, many are 4A and this is hardly high and will suit most batteries. A boost of 2 or 3 hours will allow the engine to be started and the alternator will do the rest ! If the battery is consistantly going flat there is a problem with the electrics or the battery is f dead – replace ! Modern electronic chargers will NOT charge a dead battery ! If it senses below about 8 volts – NO GO ! One way round this is an old transformer type charger and run for 15 mins or so then let the electronic unit take over once the battery voltage has come up a bit. Maypole do a very neat little 6/12v 4 A for about £28, just about to order a second one ! A lead acid battery will sulphate up in 12 months if left un used and allowed to go flat. Modern cars have many circuits that are live even when everything is OFF so will flatten a battery quite quickly if the vehicle is not used. It is a good plan to disconnect the battery if not in regular use. The alternator is a 3ph device so will give a smoother output than most chargers and will control the voltage to 14.25/14.5v, this is the running voltage of the vehicle not 12v Noel

For those of an adventuring mind, it is possible to rejuvenate a sulphated conventional wet lead acid battery that is otherwise sound with EDTA, a food addative is one of it's uses. With 100A+ batteries at over £100 it's worth a try !

Edited By noel shelley on 24/11/2021 17:14:59

Edited By noel shelley on 24/11/2021 17:31:14

[Michael GilliganParticipant @michaelgilligan61133]

I bought a Clarke AC180 at a Car Boot Sale a few years ago … It’s vintage 1999 or thereabouts, but Clarke kindly sent me a copy of the manual

This page may be of general interest :

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MichaelG.

[Author]

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