Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Dealer says can't replace factory glass matt battery with traditional flooded

Wife has a 2015 Hyundai Sonata (non turbo version). Took it in for an oil change, and the dealer said her 34-month old battery is failing. Also said it’s a glass matt battery and you can’t replace with a flooded battery or it will mess up the electronics.

This is a locally-owned dealer, and I’ve never felt like they were bamboozling me in the past, but this has me wondering. Also as they said they’d replace it for $230 today, but it would be $300 if I had it done later.

Does it make any sense that a flooded battery would mess up electronics?

I sure wouldn’t think so. Are you sure this is what’s in the car? Any starting problems? Glass mat batteries are supposed to last a long time…34 months is way too short.

AGM appears to be OEM battery type. I’d bet you won’t find a cheaper style battery that will fit and have the same performance specs. There’s a reason they chose to use an AGM battery, they can be made more compact with the same performance. Most AGMs I’ve seen have standard 36 month warranty. $230 looks like it would be a good price around here. $300 not so good. I personally love to challenge the “special price today” BS. What chance is there you just happened to coincide with a special rebate or other incentive that is good today but not tomorrow??

I doubt it would affect anything to use a flooded battery. The battery should last more than 3 years unless you’ve let it go dead. Maybe contact Hyundai directly about it.

Batteries are like tires, they have their own stand alone warranty.

I’m just referring to the AGM vs Flooded question.

What does the car’s owner’s manual say about replacing the battery, and what types are compatible, anything?

I don’t blame you for being skeptical. My fiancée’s Hyundai dealership just performed a fuel induction service she didn’t authorize and told her that her CV boots were leaking. I checked the CV boots and they’re fine.

@gh1138 Not sure I put the right info in the Walmart search but it appears they have a battery for around 100.00. I suggest doing your own internet search.

Great replies. Thanks, everyone.

I’ll have to look at the owner’s manual tonight. I’ve glanced at the battery when I check the oil and put in washer fluid. I don’t recall it being small-ish or a strange shape, but I only glance at the negative terminal to make sure it doesn’t have any corrosion, so not sure I would notice.

I tried a couple of battery finders as well. Interstate didn’t list a compatible battery, and 2 other sites listed AGMs only.

Wife clarified that the $230 price include pro-rating the 36-month warranty on current battery. The only other difference was they would waive the $20 installation fee, so at least the price difference makes sense.

In the past, I’ve always replaced her batteries at 36 months to help ensure she doesn’t get stranded, but at these prices . . .

There is a different charging system strategy used with AGM batteries to protect them from being overcharged. Your vehicles charging system is designed for use with an AGM battery, I don’t know if you will experience side affects with a flooded battery but it is Hyundai’s policy to replace with the same type battery.

Here is a Hyundai service bulletin for AGM/flooded battery service and replacement.


You can buy the exact fit battery from Autozone for around the same price as the dealer but get a full 3 year, non-prorated warranty. Full replacement cost if it fails in less than 3 years…

1 Like

I agree with Nevada_545. It’s always been my understanding that AGM batteries are charged differently. I’d stick with the AGM type to be safe, although most likely nothing catastrophic would happen if you put in a flooded battery instead.

Thanks for the service bulletin. I think that finalized my decision. With ~55,000 miles on the car, there’s still quite a bit of warranty left on the motor/drivetrain, and I’d rather not jeopardize it. I’ll go with the AGM until I’m a lot closer to 100K. Of course, by then, the price difference may be less.

1 Like

Like Nevada said, it’s best to replace an AGM with an AGM and a wet cell battery with a wet cell. I’m not familiar enough with the late model Hyundais to know if it’s possible to install a wet cell battery in place of an AGM. On certain cars when replacing a battery and registering the battery to the car, it’s required to select AGM or lead-acid and the age of the battery so the car knows how to properly charge the battery. I don’t know if Hyundai has that option.

1 Like

I recently purchased a flooded-type battery for $49 at Walmart to replace the Corolla’s battery of the same type. That one lasted about 6 years. I have no direct experience with those high priced AGM’S , but from what I’ve heard, AGM’s don’t last quite as long as a well maintained flooded battery, in part b/c they are more heat sensitive. AGM’s a also more sensitive to overcharging than the flooded-type, and presumably the alternator charging design is set up to match what the AGM prefers to avoid overcharging damage. Given all that, it probably makes sense to stick with AGM if that is what the car came designed for.

Advance Auto parts has an AGM battery for your Sonata for $221.99. They also have a 30% off coupon code SCW447 that will reduce the price to under $156.

1 Like

So all those years battery makers were touting their new expensive AGMs as a great improvement, they weren’t telling us that your car’s voltage regulation needed to be changed before you could wisely change to an AGM battery?

Some years ago Consumer Reports reported an AGM battery failed their tests, and specifically recommended against it. Now I am beginning to understand.

…and I believe their employee will swap the batteries for free (free labor that is), but I warn you the quality of the work might be proportional to what you pay for labor. If you go this route, watch him closely to make sure he doesn’t make any mistakes.

I would have to defer to the dealer expertise. I found this, may or not be relevant.

Three Misconceptions About AGM Batteries
More batteries are moving into the trunks and under the seats of some vehicles. If the battery is not under the hood, chances are it’s an absorbent glass mat (AGM) or gel cell battery. AGM batteries eliminate acid spilling in accidents because they are sealed. They can also be installed at odd angles.

Battery Manufacturers can shave off a few pounds from the vehicle because these batteries pack a lot of power for their size and weight. That’s a big ­reason why they are being found more and more on late-model vehicles.

Here are three misconceptions about AGM batteries:

You can use your regular battery charger on AGM or gel cell batteries.

False. These batteries like to be charged slow and low. Many AGM/gel cell battery chargers have microprocessors that collect information from the battery and adjust the current and voltage accordingly. Some have different settings for charging flooded, gel and AGM batteries. Overcharging can kill these batteries. Also, alternators are not chargers. Don’t rely on an alternator to do the work of a ­charger. If a battery is discharged to the point that it cannot start the vehicle, use a charger as soon as ­possible to make sure the battery gets fully charged.

AGMs and gel cells can be tested the same way as conventional batteries.

False. These types of batteries have lower internal resistance than flooded batteries. Older capacitance battery testers/analyzers may not be able to ­accurately read these batteries. Most new battery analyzers have a special mode for AGM/gel cell ­batteries. Old-school load testers might not provide conclusive results.


AGM or gel cell battery replacement is the same as flooded battery replacement.

True and False. While the installation of the ­battery may be the same for the two battery styles, some vehicles require an extra step to tell the vehicle that the battery has been replaced. Newer vehicles have a Battery Sensor Module or similar systems. These systems require recalibration with a scan tool if the battery is replaced. If the system is not recalibrated, the alternator might overcharge the new battery and cause the battery to fail soon after replacement.

This is so weird but I just bought a 2015 Hyundai Sonata Ltd. Sport, only has 7,300 miles on it. It was a leased vehicle. My 2010 paid off Sonata was hit and totaled so had no choice. After reading the above info, I checked today and the dealership confirmed what is stated above. It will cost me $230 for a 3-yr battery, or they could sell me an Allstate battery that fits in my car 2-yr for $216. Oh, well, I guess I have that to look forward to since my car is really 3 years old and it seems like I have always had to replace my battery every three years here in Florida. I never would have known. I’ll wait until the time comes. Thanks for the info. Good luck.