Maintainng Odyssey Extreme Battery

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Jun 30, 2026
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I have a couple Odyssey Extreme Group 65 batteries in my truck. They are a few months old. I would like to "permanently" install a maintainer in the truck and have the option of plugging it in when the truck won't be run for more than a few days and sometimes weeks (which happens often). I don't plan on using the "maintainer" to charge any batteries from a deep discharge.

Per Odyssey The recommended float voltage for ODYSSEY AGM2 batteries is 13.6 volts for a 12-volt battery at 77°F (25°C). They also say Regardless of temperature, the minimum charge voltage is 13.2 volts as lower voltages will damage the battery grids and shorten life.

Odyssey recommends the Battery Minder 2012 AGM. After some reading on here, I know @f355spider likes this charger. I have also read about the Battery Minder 2012. I recall a posting (I think) from @f355spider spoke to Battery Minder and they mentioned that they lowered the float voltage. I was not entirely clear if that was on the 2012 or also on the 2012 AGM? What is the typical/minimum float voltage of the 2012 AGM? Does the 2012 AG supply constant float voltage or some kind of "smart" operation when the battery is fully charged?

I recently purchased (still within Amazon return window) a Noco Genius GEN5X1. I have it hooked up and after some VERY limited testing, it seems the float voltage varies from 13.2v to 13.3v. in about 60 to 65 degree temps (no other temperature range tests done). Also, I am not clear on whether the Noco shuts off every so often and is not charging and that is the "smart" function. And if so is that bad for the Odyssey?

I sent a couple messages to Odyssey Technical asking about the Noco and received no response. I then sent a message to Odyssey sales and got a response the Noco GEN5X1 is fine. I asked if they have verified the float voltages and she responded no. So of course, my follow up was then how can you say it is fine. Her response, that is what I use at home in my garage! I would have to do more testing to see if the voltage ever drops below 13.2v.

Another option I was looking at is the Victron IP67 charger. I like Victron products and use them in my camper. With the Victron I can select whatever float voltage I want. I am not sure of their algorithm, etc and whether it is temperature compensated. I think @04GTO likes this charger.

Whichever one I select, I want to mount it in the truck. Ideally under the hood somewhere, though real estate is at a premium. I may have to mount it in the cab somewhere, but first choice will be under the hood.

The Noco wins out for permanent mount. It is designed for under hood mounting and is the smallest form factor. The Victron is IP67, so that should be good as well, though it much larger. I am not sure about the Battery Minder 2012 AGM mounting under the hood. I don't anticipate a wet environment.

Another question, can these chargers be attached to a car battery and plugged in when the car is started? I ask for the occasion where I remote start the truck from inside the house and have yet to unplug.

Thanks in advance for sharing your wisdom.
 
Update. I checked the noco this morning. It was floating at 13.07 volts in about 60 degrees.

Looks like the noco is going to be a no-go.
 
I own a NOCO, a CTEK and a victron.

NOCO. Solid plastic construction, lots of detail on the interior construction. Very conservative charge profile. Too conservative frankly. It’s the one I loan to friends. It really won’t rejuvenate a weak battery - it will half charge a drained one to get you started. Good 10A power supply mode,

CTEK. Gets hot when running. Is more intelligent than the NOCO with how it handles its voltages. Actually floats it whereas the NOCO seems to enter an on/off state. 4A is enough for most homeowner needs. Good unit. Permanently mounted but I mounted it over a plate of metal since it really shouldn’t have to get as warm as it does. YouTube tells me it’s not as well made. I really like it’s programming and it does have a gentle desulfation pulse which, when used long term, seems to make a difference… long term.

Victron. Built like a brick s- house. Solid metal case. Bluetooth gets you in to set modes or make your own. Also has a power supply mode. No front panel controls, none. It’s built to configure and walk away.

Victron for the win. If I ever need to buy something else for real, victron. If I need 1 amp to warm the mower, something cheap.

@99Superduty
 
I only tested the Battery Minder 2012AGM and it appeared to settle in around 13.4vt float at 77F/25C. When I asked Battery Minder tech support about this they said this was intentional, as they had complaints from customers of signs/symptoms of over charging during float. They claimed this change is across all models...but while I also own a couple of the 128CEC2, I have not tested them for this.

Note also that with the 2012AGM, it does temperature compensate, so I have seen the voltage go higher, even into the upper14vt range in cold temps in my garage...and it drops lower when my garage is in the 90s. The temperature compensation is automatic and continuous, so on my bluetooth monitor, I can see a smooth curve as the voltage increases overnight, as my garage cools and lowers during the day as it warms. It also has a continuous pulse desulfation during charge and float. It has been connected 24/7 on my "garage queen" Ferrari and inspite of using on a plate type AGM (H6/Group 48) from Interstate, has maintained that battery well for about 5 years and the battery tests as new. I just tested it two weeks ago. (Battery Minder recommends using their flooded setting on plate type AGMs and to only use their "AGM" maintainers or settings on Odyssey or other higher performance "pure lead" type AGM batteries)

I'm not a fan of battery tenders installed on a car...I did that once and it worked, but the battery was trunk mounted. For an engine compartment it is dealing with vibration, heat, dust and moisture. But the bigger concern is if the electronics go wonky, I see some potential for a fire. There are examples of these failing on some car forums. I saw one post of a guy that had his sitting on the carpet on the passenger side and it fried and burned up the carpet (Battery Tender brand). Fortunately the car did not catch on fire. All brands have this possibility.

Most of my battery tenders are wall mounted. If you wish for yours to be portable, just install the ring mounts that go on the battery terminals and carry the tender in the passenger compartment along with an extension cord.

Here is Odyssey's current approved list of chargers/maintainers:
https://www.odysseybattery.com/charger-comparison-tool/
 
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I know these batteries are pricey but I think they are less picky than you’d expect.

I got a used Odyssey Extreme many years ago for $20. Used it to start various vehicles, it spent some time in storage, then I soldered some cheap jumper cables onto a cheap consumer grade UPS/battery backup to extend its runtime. Worked for probably 5 years that way. I’m sure whatever charging profile that thing had (designed for a small sealed lead acid battery) was not ideal.

Eventually I tossed it in the garage when the UPS died.

Then I took it to work, express charged it, tested it, and sold it to an acquaintance for $20.

It still works fine to this day. Yes it’s like 10 years old and has been mistreated that entire time.

Just enjoy your battery and use whatever maintainer you have :)
 
Come to think of it, I had an Odyssey I purchased years ago from Sears. It was the Sear Platinum AGM but private labeled at the time from Odyssey. I had it in a Ferrari I had for about four years (until I sold the car) and it was great. It was a 34R size and I used a NAPA 1.5 amp on board battery tender on it. No issues for those four years...it was plugged in probably 50% of the time in my garage.
 
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