Flat battery /RAC /Halfords

[JohnfromUK]

Rough 'back of envelope' estimates;

A typical car battery is around 55 Ah (Ampere Hours). (Anything from around 50 to 80, big diesels are more)

A typical car 'quiescent parasitic drain' (the current it draws when 'asleep') is around 50 - 75mA.

So roughly the battery will lose 1 Ah every 15 - 20 hours, so will last around 35 - 45 days to fully exhausted.

Assume it will still start the car when it has 1/3 of its full charge remaining, and you get to about 20 - 30 days (3 or 4 weeks).  These are 'ideal' figures and in practice I think a lot would not manage 30 days, especially in winter.

 

[Sweet11-87]

10 hours ago, udderlyoffroad said:

Well let’s see: risk of damaging equipment through arcing, prematurely wallering out battery terminals (they’re only soft lead after all), It will throw up all sorts of fault codes, your fob could lose sync…

Unless it’s a car with a carburettor prior to about 1993, just don’t. Either use the car more or invest in a decent trickle charger that will keep the battery topped up

Valid points I guess and I can’t say that wouldn’t happen as all cars are different, damage to terminal or arching is user error and avoidable, error codes and electrical faults however arnt  but if I changed my car battery so in effect disconnecting it, and it picked up a fault code or lost fob sync I’d be questioning why the removal of a part that’s is in principle a consumable component that is expected to be changed during the cars  lifetime is bringing about these issues. 
 

in agreement about just rising the car more and trickle chargers can be a double edged sword. Cheap ones can damage batteries with long term use, expensive ones are the price of a new battery anyway 

[old'un]

10 hours ago, udderlyoffroad said:

Well let’s see: risk of damaging equipment through arcing, prematurely wallering out battery terminals (they’re only soft lead after all), It will throw up all sorts of fault codes, your fob could lose sync…

Unless it’s a car with a carburettor prior to about 1993, just don’t. Either use the car more or invest in a decent trickle charger that will keep the battery topped up

Agreed, also before charging look in the operator manual to see if you need to disconnect anything, with my car there is a block with a push button release connected to the minus terminal, according to manual this must be removed before charging to prevent damage to sensitive components.

[JohnfromUK]

17 minutes ago, old'un said:

with my car there is a block with a push button release connected to the minus terminal, according to manual this must be removed before charging to prevent damage to sensitive components.

Thats interesting.  I haven't seen that before.  I had a BMW (3 series estate) for around 16 years until a year ago.  The battery was deeply buried under the boot floor (and several covers) - but there was a dedicated charge/jump connect point under the bonnet.  I used a CTEK maintenance charger on it when it was unused for a longer period.

[old'un]

36 minutes ago, JohnfromUK said:

Thats interesting.  I haven't seen that before.  I had a BMW (3 series estate) for around 16 years until a year ago.  The battery was deeply buried under the boot floor (and several covers) - but there was a dedicated charge/jump connect point under the bonnet.  I used a CTEK maintenance charger on it when it was unused for a longer period.

some of these modern cars are a nightmare when it comes to charging or changing the battery, my neighbour has a 2024 Honda and that as to go back to a Honda dealer to have the battery changed.

Here's another one about modern cars, most cars now have tyre pressure censors, well according to the garage you cannot move the wheels/tyres to a different corner so you get even ware, like moving the front wheels to the back and back to the front, apparently the censors will not know which wheel is which when displayed on the dash, it will need reprogramming.

Edited February 11 by old'un

[JohnfromUK]

43 minutes ago, old'un said:

Here's another one about modern cars, most cars now have tyre pressure censors

It is common to have to 'register' the new battery as it will have a different voltage, which is needed for things like bulb checks.  Yes and when the batteries in the tyre sensors (of which there are 5 if you have a spare) go flat they are eye wateringly expensive.

[Rewulf]

Steve, could I ask what car it is, and engine type, also does it have stop/start ?

[Gordon R]

Halfords warranty:- 

 

What isn't covered by the guarantee?

The following may cause your battery to become damaged. As these issues are not manufacturing defects, they aren't covered by the guarantee.

• Sulphation: This tends to happen if your vehicle isn't driven for extended periods.
• Deep cycling: This can happen if the vehicle's engine is started very frequently or electrical consumers are left on for extended periods between journeys.
• Overcharging: This is usually caused by a fault in the vehicle's charging system.
• Physical damage: This can be caused by incorrect handling or storage.
• Incorrect application: Make sure you're using the battery that Halfords recommends for your vehicle!
• Wear and tear caused by misuse.

 

Extended periods is not defined.

Edited February 11 by Gordon R

[TOPGUN749]

Sounds like possibly the RAC man was keen to sell a new battery on commission,or that Halfords were trying to avoid their warranty obligations! Needs a full recharge for 24 hours,then a proper test with a discharge device.A rough idea of a 12 volt battery condition is the voltage held after sitting unused overnight,a good battery will show 12.6+volts,a borderline one 12.3- volts with no load at all.

[steve_b_wales]

1 minute ago, TOPGUN749 said:

Sounds like possibly the RAC man was keen to sell a new battery on commission,or that Halfords were trying to avoid their warranty obligations! Needs a full recharge for 24 hours,then a proper test with a discharge device.A rough idea of a 12 volt battery condition is the voltage held after sitting unused overnight,a good battery will show 12.6+volts,a borderline one 12.3- volts with no load at all.

Yes, either stand to make/loose on this.

[London Best]

The last battery I had to replace was fitted to the vehicle when new in 2009. I replaced it in 2022, so 13 years old. And the vehicle stood unused for 12 months in 2013/14. 
The previous battery I had to replace was over 9 years old.
 

[steve_b_wales]

39 minutes ago, London Best said:

The last battery I had to replace was fitted to the vehicle when new in 2009. I replaced it in 2022, so 13 years old. And the vehicle stood unused for 12 months in 2013/14. 
The previous battery I had to replace was over 9 years old.
 

[London Best]

We had a 1994 Peugeot 306, bought secondhand in 1996. 
In 2002 we stopped using the vehicle and it never moved until we sold it in 2004. The battery was never charged during this time. It started up with no problems. The purchaser complained after two months that she had to buy an exhaust!

[steve_b_wales]

UPDATE:

The arrogant, ignorant manager of the Halfords store has still not contacted my wife, despite their head office informing him to do so (according to them of course!)so, Trading Standards is the next port of call!

[udderlyoffroad]

1 hour ago, steve_b_wales said:

UPDATE:

The arrogant, ignorant manager of the Halfords store has still not contacted my wife, despite their head office informing him to do so (according to them of course!)so, Trading Standards is the next port of call!

To what end?

A better use of your time would be to see what the battery voltage is after an extended charge & being left to sit overnight per @TOPGUN749’s suggestion.

Or if you must, ask the RAC what their battery tester actually output. They do record these things

22 hours ago, London Best said:

We had a 1994 Peugeot 306, bought secondhand in 1996. 

An early 90s era small car, especially if it was the diesel variant I owned, fitted with an huge battery, just does not compare it terms of electrical load with any car built this century.

[Rewulf]

1 hour ago, udderlyoffroad said:

A better use of your time would be to see what the battery voltage is after an extended charge & being left to sit overnight per @TOPGUN749’s suggestion.

Ive got to agree.
There could be underlying factors with the car, battery drain through a short or a faulty module, low alternator output ect.
Blaming the battery because an RAC man said so (I have no faith in the abilities of some) testing a 'flat' battery is problematic.
I used to sell car batteries in another life, and I wouldnt replace one until it had been fully charged, cooled down and tested.

[TIGHTCHOKE]

If Halfords are silly enough to guarantee their batteries and then exchange them if you go back with a receipt, then take FULL advantage.   

[welsh1]

I recently could not start my trike, the battery was only 2 years old but it was a cheap battery sourced during covid because the usual battery wasnt available, it wouldn't turn the trike over at all (1350cc engine), when i checked it it showed 12.5 volts, but when i tested it under load it was 2.3 so it was a bad battery, usually it means some cells have failed.I bought a new battery, the one recommended and no problems.

I bet Halfords stuck a volt meter on your battery and it showed 12.5 volts or above so they think it's fine, but i bet they didn't do a load test which would show a failing cell or cells. Let's be honest most "technicians" in halfords couldn't tell a an air filter from an oil filter.

[steve_b_wales]

1 hour ago, welsh1 said:

I recently could not start my trike, the battery was only 2 years old but it was a cheap battery sourced during covid because the usual battery wasnt available, it wouldn't turn the trike over at all (1350cc engine), when i checked it it showed 12.5 volts, but when i tested it under load it was 2.3 so it was a bad battery, usually it means some cells have failed.I bought a new battery, the one recommended and no problems.

I bet Halfords stuck a volt meter on your battery and it showed 12.5 volts or above so they think it's fine, but i bet they didn't do a load test which would show a failing cell or cells. Let's be honest most "technicians" in halfords couldn't tell a an air filter from an oil filter.

That's exactly what they did! And did not do a load test, but this was checked by the RAC.

[enfieldspares]

On 10/02/2025 at 20:39, countryman said:

Best to just turn up at Halfords and ask them to test your battery, if they say you need a new one then produce your receipt.

I like it! Sneaky. But I like it!

[Rewulf]

17 minutes ago, steve_b_wales said:

That's exactly what they did! And did not do a load test, but this was checked by the RAC.

The problem with load testing (drop testing) is it doesnt give an accurate result on a low charge battery.
If it hasnt got energy energy to start the car, its pointless load testing it.

IF its got a shorted cell, it would indicate this, but then it would never hold a full charge anyway, and would always struggle.

[steve_b_wales]

1 minute ago, Rewulf said:

The problem with load testing (drop testing) is it doesnt give an accurate result on a low charge battery.
If it hasnt got energy energy to start the car, its pointless load testing it.

IF its got a shorted cell, it would indicate this, but then it would never hold a full charge anyway, and would always struggle.

I can only go on what the RAC patrolman did to test the battery condition (he tested many things) and the Halfords 'expert' just tested the battery with a volt meter. 

[Rewulf]

Just now, steve_b_wales said:

I can only go on what the RAC patrolman did to test the battery condition (he tested many things) and the Halfords 'expert' just tested the battery with a volt meter. 

And in that respect you can only go on what youre told, but I would get another opinion, as in my opinion, neither Halfords or the RAC are very good at diagnosing issues.
I could, in my 40+ years in the motor trade give you dozens of examples of utterly stupid diagnoses done by such people.

[marsh man]

Nothing to do with your problem Steve , but the last battery I bought when I had my CRV was from a Fast-Fit branch in Yarmouth , I had no problem with it and totally forgot about where I even bought it , anyhow one morning my motor won't start and the battery was flat , I stuck it on charge and by dinnertime it had enough charge to start the motor , I went over to Fast-Fit as I always have had good service from them , I asked the bloke if he could check my battery and when he tested he said it is only charging a small percentage of what it should charge , he noticed the battery was one of there's and asked me how long I have had it , I said I haven't a clue but I recon for two to three years , he took my reg and looked it up on his laptop , he came out and said it must be your lucky day as it had three weeks of warranty left , he had no more to do than put a brand new like for like battery on all done f o c with no quiddle , I gave him a fiver for fitting it and he was more happier than I was and I was very happy with the excellent service .  MM

[steve_b_wales]

UPDATE:

So far, my wife has had no joy in actually speaking to someone from Trading Standards, but, in the meantime, she went to an independent garage yesterday, and they checked her battery and informed her that there was a fault on it and that it needed replacing. This morning, we both went to a different Halfords store, and a staff member checked the battery and said that it was 'okay and nothing wrong with it'. So where do we go from here? Two have said it's faulty and two have said it's okay!

On 11/02/2025 at 11:26, Rewulf said:

Steve, could I ask what car it is, and engine type, also does it have stop/start ?

It's a 2019 MG3 and does not have stop/start.