Ctek battery maintainers & AGM batteries

[Frodo]

Is it possible to fry your AGM battery using one of these Ctek battery maintainers (aka ‘smart chargers’ I believe)?



I bought this guy over 15 years ago, shortly after buying the Boxster, since I knew I’d not be driving the car in winter weather. It has performed flawlessly—attach the leads, plug it in, choose the mode setting. It’s been used on the original battery (don’t recall what that was, probably whatever was in the car when bought new by the original owner), and on the first battery I’ve purchased for the car. That was a DieHard, which I picked up in 2014 and lasted like 9 years.

Jump ahead to Mar 2023. Replaced the DieHard with an Everstart Platinum H6 AGM. Car was kept in winter storage for a few more weeks, with the Ctek in place. Then, winter ’23-’24 car was again stored, Ctek in place (on the AGM) for the entire 4 months or so. So then, come fall 2024, I again repeated the procedure, same as always. I checked the car recently (it’s actually at the home of a friend, who goes to Florida for the winter and rents me garage space each winter) and noticed the Ctek, red Error light illuminated as shown above. On the Step 1-8 charging process, it made it to Step 5 (‘Analyze’). Per the Ctek manual, with a charging process that’s been interrupted at Step 5 it’s indicating a battery that “cannot keep charge and may need to be replaced.” I disconnected the Ctek and hooked up the multimeter; getting a reading of 3.25 V. Of course, no headlights, etc.

Last night, got to talking to my son who admitted he’d fried a battery himself. Told me that, even with the Ctek, you need to take steps to avoid overcharging. I’ve always had the thing set at the ‘Snowflake’ setting, which the manual describes as the “Cold weather program. Use for charging at low temperatures and for power AGM batteries like Optima and Odyssey.” It’s winter, it’s Ohio, it’s cold, so that seemed to be the correct choice. It’s always worked for me over the past 15-16 years. What happened this year? I thought these battery maintainers were supposed to be a ‘set it and forget it’ kind of deal? The battery’s only 2 years old, and has a 4 year free replacement warranty, but I’m not sure what I’ll be asked about as far as driving the car, charger usage, etc.

[JFP in PA]

From your information, I would say you had a battery crap out rather than a problem with the Ctek. I have multiple Ctek chargers, some for more than 20 years, and never had an issue with any of them. That said, I have seen relatively new batteries crap out in less than a year. When I replace the "new" battery with another one under warranty, everything when right back to normal.

And for the record, you cannot overcharge a battery with any Ctek model.

[Frodo]

Thank you, John. I had a feeling it would be you responding first, and that that's exactly what you would tell me.

[Burg Boxster]

Not likely to kill battery as JFP notes but possible.

I have had both a Ctek and a Battery Tender Jr. go bad on me. Rare but happens. CTek unit just stopped working - it was ~ 15+ years old so didn't really "owe" me anything. The BTJ (maybe a year old) would work for 2-3 minutes (I found out later after working flawlessly prior) and then go into fault. Subsequently did a great job draining a 1yr old AGM battery. Costco refunded the BTJ and helped cover cost of new power plant - battery was perfectly fine before but obviously compromised w who knows what discharge caused by BTJ.

Simple test would be to put Ctek unit onto another vehicle and see what happens and go from there.

Good luck

[JFP in PA]

You can also have the battery load tested, but from your description, it sounds like it is toast.

[Frodo]

Originally Posted by Burg Boxster

Simple test would be to put Ctek unit onto another vehicle and see what happens and go from there.

Good luck

Do you not risk ruining that battery?
I guess you intermittently multimeter that battery to see if it's being drained..

Or, just watch to see if the lights proceed all the way from Step 1 to Step 8 maybe.

I may try this in my other vehicle, my daily driver. It's got a battery that's like 6 years old. I checked it the other day; it was reading like 12.2 V (so I suppose it's getting near to needing replaced?).

[Frodo]

Originally Posted by JFP in PA

You can also have the battery load tested, but from your description, it sounds like it is toast.

I suspect you're right.

When I take it back, you think they'll ask me anything about its history? Daily driver? Stored, on a battery tender? I got it at Walmart—I guess they may not ask me anything, long as I've got the receipt (I do).

[Burg Boxster]

Originally Posted by Frodo

think they'll ask me anything about its history? Daily driver? Stored, on a battery tender? I got it at Walmart—I guess they may not ask me anything, long as I've got the receipt (I do).

My $ says no questions asked. You'd be lucky to find a WallyWorld associate w/ enough knowledge regarding... or concern. They'll simply check receipt against purchase and eligible warranty.

Good luck.

[Burg Boxster]

Originally Posted by Frodo

Do you not risk ruining that battery?
I guess you intermittently multimeter that battery to see if it's being drained..

Or, just watch to see if the lights proceed all the way from Step 1 to Step 8 maybe.

I may try this in my other vehicle, my daily driver. It's got a battery that's like 6 years old. I checked it the other day; it was reading like 12.2 V (so I suppose it's getting near to needing replaced?).

I wouldn't leave unattended - if maintainer is issue it should fault relatively quickly after start up.

That said, 12.2v on a daily driven (assuming at least good 15min trips) = you're on borrowed time...

Good luck

[Frodo]

Got the battery exchanged, one question asked ("Do you have a receipt?"). So, piece of cake.

Decided to throw the Ctek on the Subi (dd) battery, which was the one that had been at 12.2 V. In under 2 hrs it indicated "fully charged" (Step 7 on the Ctek). Multimeter indicated 12.7 V...so, who knows, maybe it'll stick around for a while!

[JFP in PA]

Ctek make quality hardware.