Older CTEK Battery Tender OK To Be Used With An AGM Battery?

it may cutoff and go to float before fully charged since AGM have a standing higher voltage .. it is ok to use but not ideal since you will keep battery at a level less than 100% .. also at .8 amps it isn't very powerful just in case you do deplete it somewhat
For less than 100 dollars get a mxs 5.0 and you will be better off

 

AGM batteries are more sensitive to overcharging compared to normal lead-acid batteries. Your CTEK should have an AGM mode on it- it's the snowflake logo on mine. Check your manual to be sure.

 

I believe the snow flake is a newer feature that senses the ambient temperature and adjust the program/voltage accordingly

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That could be true- mine is an older CTEK (Multi US 3300). This is what it says in my manual:
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You should be able to get a copy of the manual on their website. They also have a way to contact them and they can provide a bit more guidance on what to do. I asked them on my tractor battery as its not really a motorcycle battery nor is it a car one either. Additionally there is also the manufacturer of your battery to contact, too.

For what it's worth my friend used a CTEK on his Ferrari (360CS) with an AGM battery and used the Snowflake mode for years and never had a problem. He has a different tender than mine though.

 

Hi Dave I think I found your CTEK manual? You should be good...
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Tender: https://smartercharger.com/collections/car-battery-chargers/products/ctek-us-0-8
Source: https://cdn.shopify.com/s/files/1/0117/5237/4372/files/56-865-US-0.8-NG-Manual-Print-file-001.pdf?7329607522301633849


However please note... I am just some guy on the internet. You should verify this with the manufacturer of your battery and CTEK just to be sure.

 

I have both CTEKs: the no frills 0.8A and the 5A with all bells and whistles. Long story short : the 5.0A is the best CHARGER, but as a TENDER the 0.8A is better.

Of these two, the cheaper is the one I prefer: it does not overheat and I can let it plugged for months whereas the more expensive one seems to be more sensitive to power outage (it will throw out an error and stop charging until I come back, which can be quite a few weeks in winter).

As said the beefy one can recharge a fully depleted battery much faster, but the 0.8A charger can nonetheless take care of very large batteries. I am even using it on a Excide EA900 (so a 90Ah battery).

So if you want to plug the tender and forget about it, the 0.8 is less troublesome.

 

Sounds a little like post 2 [emoji848][emoji38]

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The difference between the CTEK US 0800 and the MXS 5.0 (or MUS 4.3 or US 3300 series) as I understand it, is that the 0800 only applies a nominal absorption voltage of approximately 14.4V, rather than the optimal 14.7-14.9V max. that an AGM prefers for full/optimum charging. As a float charger/maintainer, it's just fine and doesn't exceed allowable AGM ranges. I've been using US 0800s on AGMs successfully - primarily in motorsport applications, but slowly migrating to the higher current/voltage versions

Stage State of
charge Voltage for 12V nominal AGM batteries

Charging rate
1 Bulk 0…80% 13…14.5V,
rises 0.1C (normal),
0.2…0.3C fast
2 Absorption 80%…100% 14.2…14.9V declining
3 Float 100% 13.2 … 13.8V very small
controlled
reference

 

That's correct, but in any case the 0.8A charger also includes the burst charging technique that breaks up the dendrite inside the battery plate. This technique condition the battery just like overcharging it to 14.9v. Now you can use both (burst charges and over-voltage charge) if you use the 5A charger. Overcharging is more important for spiral wound batteries (such as Optima) as these do have so tightly packed lead plates, that you'd better keep them clean in order to avoid internal shorts.

Unless the OP has an Optima, I think he is fine with the charger he already has. Just my 2cts.

 

Just to pile on, the Ctek the OP has will work just fine. The are many newer features now, that include automatic temperature compensation, as well as specific charging profiles for AGM, Lithium Ion, and normal flooded batteries.

I've been researching a ton on this, as I updated some of my maintainers late last year. Be aware that only a select few AGM battery manufacturers recommend the higher charging voltage of 14.7 or the higher float voltage of 13.6. Usually it is Odessey that specifies this. For most other AGMs the normal flooded battery setting is fine. I spoke with a tech at Battery Minder and they say you should only use their AGM setting with Odessey and Optima...and flooded setting for other AGMs or you may experience overcharging. Many battery maintainer companies do not share their charging and float profiles...some do. In testing, I found that most float around 13.2vt to 13.3vt. Some additionally "pulse" the voltage every few minutes, claiming it reduces sulfation and may give a higher state of charge.

Some maintainers will turn off the float charge and wait for the battery to drop to some lower voltage then begin charging again. This is supposed to "exercise" the battery. Some people don't like that profile, as it may leave the battery in a less than ideal state if you randomly need to use your vehicle and the battery is dropping down and hasn't hit the point to start the charging again...so you are starting your trip with a battery someone discharged.

Automatic temperature compensation is a newer thing for maintaining during float charging. The maintainer will automatically raise the voltage (incrementally) when float charging as temperatures get colder, and lowers the float charging voltage (incrementally) when ambient temperatures increase. Only a few companies offer this feature. Some use a simple button you push at lower temps (Ctek) that increases the charging and float voltages...but it is a preset amount, not incremental, and has no effect at higher temperatures, meaning it can overcharge when your garage temps are over 80F.