Smart chargers and really flat batteries

[Orionaut]

Modern smart battery chargers will not start charging unless there is a minimum terminal voltage present.

Which presents a problem if one is attempting to charge a really flat battery.

One can get round this by putting a good battery in parallel to the flat one to get the charger to cut in.

But this can be a bit of a faff.

Does anybody make a charger that can be overridden in some way to allow a really flat battery to start charging??

 

[sovietspybob]

Isn't the reason they won't charge a really flat battery is that when a regular car battery goes below a certain voltage (anything lower than 10.5 volts usually) it'll be permanently damaged and won't ever hold a charge properly so you should really just replace it at that stage.

 

[Orionaut]

Isn't the reason they won't charge a really flat battery is that when a regular car battery goes below a certain voltage (anything lower than 10.5 volts usually) it'll be permanently damaged and won't ever hold a charge properly so you should really just replace it at that stage.

Shouldn't be, I have recovered many batteries from far lower states of charge than that and they have subsequently tested out just fine with my Midtronics type tester (Conductance tester) and they have worked just fine in practice.

Sure, deep discharge can destroy a battery, especially if it is left that way for weeks on end, but a flat battery from leaving the lights on overnight (Say) which can easily discharge to below 6 volts is usually recoverable with no obvious long term damage if the battery was previously otherwise OK.

 

[Bluecube]

My two smart chargers have options for regenerating completely flat batteries. Only have to use the option a couple of times but it worked. May be worth checking the manual to see if your charger has similar options.

 

[Clarkey]

Isn't the reason they won't charge a really flat battery is that when a regular car battery goes below a certain voltage (anything lower than 10.5 volts usually) it'll be permanently damaged and won't ever hold a charge properly so you should really just replace it at that stage.

Nah that's nonsense, I've charged multiple batteries from completely dead and gone on to use them without issue for years.

 

[Scythe]

The CTEK MXS 5.0 has a recondition feature to recover deep-discharged batteries aside from its normal smart charger function.

https://www.ctek.com/products/vehicle/mxs-5-0

 

[MatteH Oxford]

You can use a 9v PP3 to start the charge instead of another 12v in parallel.

The reason why it won't charge without a voltage present is to prevent the charger leads shorting together when not connected to a battery, if the charger is plugged in to a wall socket that's switched on.

 

[Orionaut]

My two smart chargers have options for regenerating completely flat batteries. Only have to use the option a couple of times but it worked. May be worth checking the manual to see if your charger has similar options.

Mine has a similar function, but it still wont cut in below 6 volts or so. I am guessing it is to do with reverse polarity protection. Below a certain voltage, the charger cant make the connection to even see that a battery is present.

(I dare say more expensive smart chargers are somewhat smarter than mine)

Obviously, if one did have a manual override, one would have to use it very carefully

And yes, I did come across somebody once who had managed to charge up a dead flat battery the wrong way round using an old fashioned "Dumb" charger. Surprisingly it did work really quite well afterwards, but just with the polarities reversed

 

[Bluecube]

It wasn’t a manual override. It was a specific function for reviving “dead” batteries so should be safe for general use.

 

[Lopéz]

Nah that's nonsense, I've charged multiple batteries from completely dead and gone on to use them without issue for years.

Whilst I'd broadly agree, that's becoming less and less true. I'm not sure what's changed over the last few years in modern lead acid batteries, but they really don't take multiple discharges like they did 10-15 years ago - particularly at the lower end of the market.

Even if they recharge to 12V, quite often the CCA is completely shot.

 

[jpaul]

I've had a similar issue changing nimh in houeshold products - razers/toothbrushes

but they really don't take multiple discharges like they did 10-15 years ago

they are adding calcium and other alloys, even in cheaper batteries electrodes, that may make them less resilient if you don't have a smart charger limiting the current

 

[Clarkey]

Whilst I'd broadly agree, that's becoming less and less true. I'm not sure what's changed over the last few years in modern lead acid batteries, but they really don't take multiple discharges like they did 10-15 years ago - particularly at the lower end of the market.

Even if they recharge to 12V, quite often the CCA is completely shot.

It's funny you should say that. I would say my experience is the opposite, years ago a deeply drained battery would be toast but the newer ones from the past 10 or 15 years seem to take well to a recharge. I've never used anything more than a 4A charger. I only recently got a 'smart' charger, as mentioned in the OP, it's annoying you have to jump the battery the make the charger kick in with it.

 

[bainbridge]

An old analogue charger does the business. You can overcharge too in order to recover some capacity on old batteries.

 

[Dogbreath]

Isn't the reason they won't charge a really flat battery is that when a regular car battery goes below a certain voltage (anything lower than 10.5 volts usually) it'll be permanently damaged and won't ever hold a charge properly so you should really just replace it at that stage.

The reason chargers want to see a minimum voltage before they start charging is simply down to polarity protection.

 

[jpaul]

*mild reboot*

Any recommendations for a mains trickle charger via cigarette lighter ?

Older neighbour has a Ford Ka, used irregularly for short distances - they're not too worried about the wear on the car, but could do with something in the garage to just plug in when they garage the car.

Can you just get an adapter for a smart charger ?

interesting - hadn't realised ctec smart charge was so complex

 

[dale1uk]

*mild reboot*

Any recommendations for a mains trickle charger via cigarette lighter ?

Older neighbour has a Ford Ka, used irregularly for short distances - they're not too worried about the wear on the car, but could do with something in the garage to just plug in when they garage the car.

Can you just get an adapter for a smart charger ?

interesting - hadn't realised ctec smart charge was so complex

Is the accessory/cigarette lighter socket constantly live in a Ka? If not and it's only on with the ignition then charging it via the socket won't work.

If it is constantly live then ctek sell an adapter that works with all their smart charges up to 5a

 

[chaparral]

The CTEK MXS 5.0 has a recondition feature to recover deep-discharged batteries aside from its normal smart charger function.

https://www.ctek.com/products/vehicle/mxs-5-0

A CTEK MXS 5.0 charger Will only charge a 12volt battery if it over 2 volts

 

[jpaul]

Is the accessory/cigarette lighter socket constantly live in a Ka? If not and it's only on with the ignition then charging it via the socket won't work.
If it is constantly live then ctek sell an adapter that works with all their smart charges up to 5a

indeed I need to check cigarette lighter is live;
neighbour wouldn't be able, to delve around under the bonnet, for attaching battery clips.

Maybe ctek's are well 'protected', but I would never charge a battery in the car, without removing its earth/car connection, first, too, just in case the charger sent some pulse to the ecu (would your fully comp car insurance cover that, i guess so),
on the other hand, if it were a dedcated cigsarette trickle charger, I'd expect it to avoid that issue.

 

[thecremeegg]

Just jump the car and run it for a few mins then take the battery inside to charge?

 

[jpaul]

In my case neigbour is 75+ years old, takes the Ka out for short trips, where more charge is lost, than gained,
they are best of friends with the AA home-start, and wouldn't be able to remove battery ...
(hell) it even annoys me if I have to reset the clock, and the presets on the car car radio.