Sound like dead battery?

mnbvcxz

Out of the blue car wouldn't turn over. Battery turns out to be 12.2v but if you try and start it instantly collapses to 8.somthing volts. Then after a while it recovers to 12.2v. 

Car works fine if jumped but driving around  for twenty minutes still didn't leave battery with enough oomph to start it on its own. 

Charged battery with ctek charger, error red light first attempt but second said it worked. But after charging same problem... 

I ordered a new battery. Hasn't arrived yet. Now second guessing myself. Last time I replaced a battery on another car it turned out to be the alternator dying...

Does this sound like a classic dead battery? 

Thanks.

Mildly_Miffed

That kind of voltage drop could be a knackered battery with no ability to deliver current - or it could be poor connections, perhaps on the earth lead.

Rule out the earth lead by putting a jumplead between engine and battery -ve.

Rule out the alternator by checking voltage with the engine running. It should be 14.5v or so.

CliveOfIndia

How old is the battery?  If it's older than about 6 or 7 years or so, it's quite possible that it's had it.  Yes, it could be a problem with the alternator - the previous poster has given some good tips for checking that.

Hopefully it will turn out to be just the battery, which is a relatively cheap and simple fix (well, OK, I know batteries aren't exactly cheap, but less expensive than some of the alternatives!).

mnbvcxz said:

Charged battery with ctek charger, error red light first attempt but second said it worked. But after charging same problem...

This, to me, would strongly suggest a battery issue, assuming all the connections are OK and it's not just being caused by a loose connection somewhere.

mnbvcxz

Thank you mildly miffed. Yes after jumping it the running voltage is 14 something volts. I tried your idea of putting a jumper cable from the negative terminal to an unpainted bit of engine but it did not make any difference. Despite starting at 12.6v (I have been trickle charging it) it instantly dropped to 8v and just clicked. 

Clive of India, sadly I can't work out how old the battery is. It just says a yigit aku. Whether hyundai would have included that as original, who knows. Car is six years old so someone may well have replaced the original one a few years ago. If it is the original battery it has done reasonably well.

Yes batteries are not that bad. I made the slight mistake of asking do you want an odd brand for £40 from the local store today or a smart brand for twice as much by mail order in a couple of days. And they chose the smart one so a the finest bosch battery is coming. It may be worth it. 

Anyway reading up people do say modern batteries can just fail suddenly with no warning or lights which makes me feel a little better. So perhaps it is just that.

Thank you for the ideas. We shall see.

Thanks

Ectophile

I have had batteries that fail the usual way - they get weaker and weaker until one cold morning they can't start the car.  A good charge may recover the battery for a few days, until the next cold morning.

But sometimes a battery will fail suddenly, as something breaks inside.  One moment, it's fine.  The next, it will just about power the ignition system, but the voltage collapses the moment you try to start the car.  No amount of charging will fix it.

It sounds like you may have the latter.

A healthy alternator should put out no less than 13.8V and no more than 14.4V.  If you're getting a little over 14V, then the alternator isn't the problem.

Goudy

Reading the voltage of a battery will only give a part signal of it's health as it's not really the volts that start the car, it's the amps and it's performance is based on how it can store and deliver enough amps to start the engine.

You can after all get a tiny 12v battery not much bigger than a double A battery, but that won't start an engine as it has only a few milliamps.

A car battery has to be the opposite, it has to supply a large hit of amps, so your average car battery is designed to store 50, 60 or more amps but have the capacity to multiple that by around ten times for short periods (this is called Cold Crank Amps or CCA).

So it's can struggle along light on volts as long as it's still got the capacity to deliver enough amps to start the engine as manufacturers tend to fit batteries with slightly more CCA's than they actually normally need as a car is likely to be operated in different conditions, hot, cold, freezing etc.

It's harder to actually DIY test a car battery for amps.
Your standard digital multimeter set to read amps just won't be able to cope, even the amps in a knackered battery (one that fails to start the car) will fry it.

There are tools that place a load across the cells and that measure the current released.
They can be had for less than £20, but most garages will be able to test one for you for free if they are not too busy.
Some national fitting and accessory chains will also do it, but remember they do sell batteries!

You can get an idea of what's going in with a voltmeter, by measuring how the battery recovers after starting.
If it struggles to spring back to normal soon after starting then it's likely knackered, but it all depends on the effort to start.

It takes more out of the battery to start a cold engine than a hot one and temperature of the battery also has an effect on it's abilities.