It's probably a bad regulator in the alternator. What is the battery voltage after sitting over night and before starting?

That high of a voltage usually indicates very strong acid from the water being boiled out. It has probably ruined the battery.

 

That was kind of my reasoning as well. If I've driven the car for a bit, and shut it off, it'll usually fire right back up with no hesitation.
The first start of the day, or if it's colder at night, it sounds like a dying battery trying to start.

 

Does the battery have any caps to add water?

 

No, it's a sealed unit. If it wasn't only a year old, I'd pop the sealed areas and check water. I may still...

 

Does your SRS/Airbag light stay on after the engine has started? Voltages greater than 16V should log a code in the Airbag ECM causing the warning light to remain on.

What's the voltage across the battery during engine crank? If the engine is cranking slow but your meter is showing more than 10V across the battery, I suspect your meter may need recalibrated.

 

No. Airbag light stays off. Tested battery with both analog and digital meters, same result.

 

Tested battery with both analog and digital meters, same result.

And the cranking voltage was?

 

If it's an AGM battery you won't be able to access it without tearing it up. May have been underfilled at the factory as they take a precise amount of electrolyte. That too would show a high voltage if the acid is strong enough. But if the alternator was over charging the result is the same.

When the yellow top spiral batteries first came out a friend had one that swelled all up and started shooting off smelly fog through the vent. Smelled and looked like a volcano.

 

I honestly can't recall the exact drop, but it wasn't more than @ 1-2 volts. The battery should theoretically be able to crank that starter no problem, but it definitely struggles sometimes. That's why I'm thinking it's alternator based.

*just double checked. Battery does have access plugs. Checked fluid level; all plates are covered. How far above plates should fluid be; since it apparently has enough fluid, is a bad alternator still the likely culprit? Incidentally, I appreciate the helpful responses so far.
Ed

 

Battery fault tricking the alternator into ramping up juice..

OE battery from 2008-2009.... replace it !!

It a wonder you aint started popping filaments of light bulbs..

Start it up, and remove 1 battery cable from battery to remove the "load".... test voltage again at cable ends without battery and see what we have..

 

Battery was replaced in December of last year.

 

Where? Most any battery has 12-months non-pro-rated free replacement. Go back where you bought it, let them test the entire system. Replace the battery since it should be free and re-test and see what the alternator is doing.

Checked fluid level; all plates are covered. How far above plates should fluid be;

Really as long as the plates are covered, you are fine, but ideally, you want it up to the level of the split ring (where the fluid will look concave instead of flat when you look at it), but don't overfill it to where it leaks out ...

since it apparently has enough fluid, is a bad alternator still the likely culprit?

Too early to tell

 

We've had some random "CRAP" batteries...

 

Agreed. The abnormal voltage readings make me think alternator. The labored starting makes me think battery....

 

Not sure what type of alternator is used on the MC Accent. If it's a battery sensed type, high resistance on the sensing wire can cause the alternator to over charge. The sensing wire sends feedback about the battery terminal voltage to the alternator. If there is high resistance (or a blown fuse) on the sense wire the alternator sees the battery voltage as being lower than it really is which causes the alternator to ramp up it's output voltage to try and bring the voltage on the sense wire back into spec.

Have a look on the back of the alternator. You should see the thick main cable and a connector with one or two thin wires. If it only has one thin wire (warning light wire) on the connector it's a machine sensed alternator. If there are two thin wires it's probably a battery sensed type. You'd want to do a voltage drop test on the sense wire before replacing the alternator if there are two wires on the connector. The warning light wire is usually blue and the sensing wire is usually red.

 

Thanks for the detailed response. I'll have to check that tomorrow, as I ran out of daylight today, but I'll try your suggestions and go from there.

 

If your alternator is putting out 17.5 volts its defective and it can blow fuses.

 

If your alternator is putting out 17.5 volts its defective.

No, it might be defective. You can't say for sure until you test the circuit. That's the mistake the guy with the Sonata Alternator Issue made too. Replaced the alternator without testing the wiring.

 

Sure, checking all the circuits first is natural before any replacement. I just found out that hyundai put substandard positive battery cable--maybe just a bad batch Idunno. So, that is a new factor I need to consider with hyundai cars. Still, an alt putting out 17.5 volts is way over. Its a prime suspect.

 

Your are right. But you'll surely can blow some switches, bulbs, other circuits. Point is, 17.5 volts its excessive for the system.

You can load test the alternator by turning on your ac, headlights, and all the electric accessories you have. Then get the reading from your voltmeter/multimeter.

 

I'll try that as well. At this point, I think it's either a bad battery or bad alternator.

The confusion for me is the occasional hard starting, coupled with the high voltage readings.

 

Why haven't you gone to AZ or O'reilly to get a free starter,battery,alternator test?

The way I see it, if the alternator has been putting that much voltage through your battery since you got it, its fried now. Hence the hard start. You will be needing a new battery and alternator. I don't think there is really that much mystery to this problem. The longer you drive with that alternator, the more problem will crop up. I am surprised that you don't see any weird electrical anomalies like brighter lights. Batteries has a warranty of 3 years full replacement usually, so no expense there hopefully. Just take it back where you got it. But, I would change the alternator first so as not to screw up the new battery again.

 

A battery that has failed due to over charging won't be replaced for free under the manufacturer warranty. That's like crashing your car then expecting Hyundai to replace your airbags because they deployed.

 

Maybe not in the UK - here in the USA, it likely will. I know for a fact you can leave your lights on overnight (well, not on a 2016 Accent) and they will replace the battery (maybe not Hyundai, but AutoZone, Advance, O'Reilley, Wal-Mart) without question.

I think it is a combination of:

• It's too hard to determine WHY it failed and they don't want to take a chance that the battery was defective and now (if it was A/Z), you are mad at A/Z and will never buy from them again.
• New battery sells for probably $75-$125 but manufacturer cost is likely $10-15 - so they can replace it 6-7 times before they lose money.
• It's somewhat of a shakedown for them - i.e. the new battery is $75-125, but costs them $10-15. Typically it lasts more than three years, which is the free replacement period. Beyond that, it is pro-rated, so they might sell you a replacement for $50 - which they still make money on. (And since you bought it from them, you are more likely to return there to get it tested and if it ends up being the starter or the alternator and not the battery, you are more likely to buy that from them since you are already there anyway ...)

 

As long as the plates are covered that is good enough for fluid level.

 

I thought so too. I'll keep this post updated as to what I find; I appreciate all the feedback thus far.
Ed

 

Is there any acid on top of the battery? It should be gassing quite a bit with 16v going into it.

 

You read WAY too much into my comment, but things are also different here ...

It won't be a shop keeper ...

The clerk/receptionist/salesguy/cashier (typically does all of those) will wheel out something like this:
https://www.otctools.com/products/minuteman-plus-battery-tester-0

It will likely load test the battery and show it is bad and test the alternator and show it is 17V and has a bad regulator.

Now what I said is the shop won't say the battery can't be warranted b/c the alternator was bad also. Really it can be hard to tell if the V/R in the alternator failed and allowed it to overcharge the battery, or if the battery failed and caused the alternator to go into overcharge mode (but 17V seems high even in that case).

The shop will warranty the battery and probably say you need an alternator.

Now - when you get into denying warranty claims is when the customer says "Okay, I can't afford and alternator now, just replace the battery" and then comes back in 2-3 weeks to get THAT battery replaced under warranty.

 

The clerk/receptionist/salesguy/cashier (typically does all of those) will wheel out something like this:
https://www.otctools.com/products/minuteman-plus-battery-tester-0

It will likely load test the battery and show it is bad and test the alternator and show it is 17V and has a bad regulator.

And that's the problem. 17V at the battery doesn't necessarily mean the regulator/alternator is bad. (see my earlier post about battery sensed alternators). You need a tech with the correct knowledge to diagnose the system properly. Having a fault on your car "diagnosed" by a shop clerk/receptionist/salesguy/cashier is a bit like calling out a plumber to rewire your house.

Now - when you get into denying warranty claims is when the customer says "Okay, I can't afford and alternator now, just replace the battery" and then comes back in 2-3 weeks to get THAT battery replaced under warranty.

If the customer insisted on replacing the battery I'd be explaining to them that the replacement wont have a warranty since it's being fitted to a vehicle with a known over voltage charging system.

 

Costco does not even bother checking their batteries. You take the battery (within 3 years) to their return counter and get a full refund. Then go get another one off the shelf. Other stores like AZ, will usually check the condition of the battery, but you can just take it off your car from their parking lot and put it in their counter for checking. Obviously, in OPs case, its a bad one. I don't part swap when diagnosing, but this is one of those exception where its quicker and free to just exchange the battery just to eliminate it from the equation. Should the OP get the alternator from say AZ, that one will have a lifetime warranty till you own the car. Should it fail, just return for a new one for free. Another example of parts swapping integrated to diagnosing problems because its free. Of course they will check that before giving you another one.

I am pretty sure the alternator on the accent is just the regular alternator commonly found in the US. I think you call it machine sensed? Can you find out if its battery sensed?