How to test a dead car battery & not just a flat one?

JustAnotherSaver

Car been causing no problems whatsoever.

Went on a fair drive at the weekend. 1hr either way. No problem.

Not used since Sunday. Not common but not drastically unusual either.

Car wouldn't start. Unlocked on the keyfob but then wouldn't lock on the remote.

Would just click-click-click when turning the key. No effort to start. Radio not working.

Plug in opcom & car is showing as 8.7v. Battery on charge.

No lights left on & everything else that's a power drain turns off with the ignition anyway.

Battery is a '4yr' Halfords one fitted Sept 2018 so fair enough it's coming up its time but at the same time wouldn't have thought it'd just totally die out of the blue this early.

Question is, rather than assuming the battery is dead-dead because it's a '4yr' one & we're 6 months short of that, how do you actually test to see if the battery is dead & not just flat?

Although if it is just flat, I wonder how since nothing was left on.

Benny2020

Have you got a battery charger or able to borrow one, the charger i have has indicator lights on it to tell you the battery health and charge level.

[Deleted User]

Easiest just to see how it is after a charge. Depending on the charger involved you could be looking at 20+ hours though to fully recharge from that state.

However does sound a lot like something untoward has discharged it since it was last used to get it right down to 8.7v especially if there were no prior warnings such as sluggish starting or warnings on the dashboard - maybe some kind of parasitic drain on the battery - knowing the car make / model might provide some clues as some have known faults that cause this to happen suddenly.

After charging, if you have a multi-meter you could check the current draw to see if that was the issue. 

JustAnotherSaver

JustAnotherSaver said:

 Battery on charge.

Benny2020 said:

Have you got a battery charger or able to borrow one

[Deleted User] said:

After charging, if you have a multi-meter you could check the current draw to see if that was the issue. 

I have one but don't particularly know how to use it to be honest. How would you test that?

This is the charger I have.

[Deleted User]

Nice, the ctek chargers are great, the indicator lights on the charge cycle will help tell you if there is an issue.

So from another post I know what car you have, that battery will need around 24 hours to charge fully with the 3.8 amp ctek, even longer if you go through the recon modes.

I can also guess you might have parasitic battery drain from one of two common things on similar Ford's of that era, the alarm module or bluetooth module.

Checking is a case of disconnecting one of the battery terminals and putting your multimeter across it in amp mode. Don't switch anything on though as it will blow you multimeter fuse, come back an hour later to see the current draw, should be 20mA ish 

https://www.wikihow.com/Find-a-Parasitic-Battery-Drain

forgotmyname

A dead battery will fail most tests, thats why its easy to sell a new battery at the roadside. Jumpstarting the car

and running the engine for a few minutes is highly likely to result in a battery that does not have enough

capacity to pass the tests.

A good charge and then testing the battery may find its actually serviceable. Depends on the age and why its flat.

Fairly new battery with the lights left on for just a fraction too long then it should recover. Older battery not fully

charged often then it may have lost its capacity.

JustAnotherSaver

@[Deleted User] sorry this isn't the Ford. 
This is on an Astra H. 

As for the modes, I just plugged it in. I didn't press mode. 

Nunber 1 & 2 lit up but that was it. Then I left it. 
Haven't yet checked it this morning. 

Goudy

You need a load test done on the battery. This is often called a drop test or a deep cycle test.

You need more than volts in the battery, you also need amps and while it's quite easy to test for these volts with a simple voltmeter or multimeter, load testing is a bit more difficult and requires a specific tool.

These tools basically draw amps from the battery and a good battery should be able hold around 10v when half of the battery's CCA's are drawn over 15 seconds.

It's possible to charge a battery and get it to read 12+volts yet it's ability to store amps is compromised usually due to dead or underperforming cells in the battery.


There are other tests you can do before the load test that may discount the need for it.
If you rule everything else out, then all that's left is the above!
 
You can test the alternator output with a voltmeter/multimeter.
Run the engine and prode both battery terminals with the meter set to read volts.
You should see very near to 14.4 volts with the engine running and no electrical load on the system.

If you increase the electrical load, say by turning on the high beams, heated screen etc, the volts should dip a little at first than start to return back towards 14v or so.


If you test alternator and it appears good yet is still going flat there is a possiblity there is a parasitic drain somewhere.
You can test for this with a multimeter set to read (small) amps.

Turn everything off, engine and electrical, close doors (window open) etc and disconnect a battery lead.
With the multimeter set to amps, bridge the gap between the battery post and the disconnected lead.

With everything off you should only see a tiny amount of amps being drawn off, somewhere around 0.05 amp.
It might spike a little when you first connect but it should settle to an even draw.

Anything much higher and you have a drain somewhere, now it's down to pulling fuses until you find the circuit that's the problem, then checking the items that are on that circuit.
Though if you have just fitted a new head unit, that's where to start as it's often been wired incorrectly (switched live of the head unit that's connected to a permanent live feed)

mobileron

Check the warranty on battery note that Halfords have been offering 4 years.

JustAnotherSaver

Can't find the receipt (usually keep them) but stranger than that is I can't find my e-receipt (don't delete emails) yet I have receipts in and around that timeframe.

Anyway, using the above charger the battery was on charge for around 39-40hrs. Never got #7 on the charger to light up but it lit up the way to #6.

Started it up with the multimeter on and it was showing 14.4v so I take this is saying the alternator is doing its job.

Went for a bit of a drive. Maybe about 8 mile or so say.

Car then sat for about 7 hours. Multimeter back on & it's reading 12.45v.

[Deleted User]

For the Ctek charger with 8 lights, if you got past light 4 then it is fully charged, 5 is analysis to check whether it holds charge so if you got there is was fully charged. Light 6 is recondition if you selected that with the mode button, 7 is float for long term.

Suggests it was doing a recondition which blasts the battery with 15.8v at a low current.

Depending on the accuracy of your multimeter, 12.45 suggests about 75% charge status so is a bit low considering you've just fully charged it, 12.6 - 12.7 is fully charged so would expect nearer to that.

Check again in another say 10 hours and see what it says, wouldn't expect it to drop over that time.

I'd be doing the standby current draw test anyway as per the link in my earlier post if you want to get a result now as to whether that is the cause of the flat battery.