AGM Battery Charger – a missing tool.


The majority of experimental aircraft use Absorbed Glass Mat, (AGM) batteries, the most common brand for the last 20 years has been the Odyssey, recognizable by it’s orange top.  For as common as these are, the majority of people using them miss the important detail that they should never be trickle charged, and the have vastly better performance and lifespan if you use an AGM specific charger. 



Pictured above is a BatteryMINDer 128CEC1. This is a good choice for an Odyssey battery. This particular one keeps the Odyssey 680 battery in Phil Maxson’s 601XL topped off at my place.  They are not cheap, but they are the correct tool for the job. 


The moment I share this, someone will comment that it isn’t required, that they have never used one, etc. That is their opinion. In experimental aviation, you will face 100’s of occasions where the path boils down to “Do I follow the specific recommendation of the engineers who designed the part, or do I follow the advice of a guy on the net who I have never met in person, who is telling me I can save some money?”  I have worked in Experimental aviation for three decades, and I can tell you where each of these paths lead in the long term. Even if this is your first month in homebuilding, you can probably guess the destinations of each mindset. 


Full Disclosure: I don’t sell batteries nor charges, I have no sponsorships nor hidden dealerships, I have no friends who do these things either. My website shows that I’m obviously a dealer for some aviation products like Rotec carbs and Warp Drive props, but unlike many people offering ‘friendly advice’,  I pay regular price for all the stuff I comment about.  My comments here are solely based on using AGM batteries for 25 years……..Oh and reading the instructions written by the engineers that made them. 


William Wynne

3 Replies to “AGM Battery Charger – a missing tool.”

  1. A Battery MINDer *is* a trickle charger, just a specific kind, and you’re right, is the correct tool for AGM and gel batteries. If you are only interested in maintaining a battery, the 1.5 amp Battery MINDer is about 1/4 the cost of the 8 amp version you mention. There is also the Battery Tender brand, which is almost as good but lacks the desulfating function of the Battery MINDer.

    It’s not just because some authority thinks so, the reason for the different charger requirement for AGM and gel batteries versus flooded is fairly simple. Because of small variations in the electrolyte and plate separators, the current density can change over the surface of the plate, leading to spots of lower and higher resistance. With an uncontrolled trickle charger, this can lead to hot spots where the electrolyte is starved more than usual (in the case of AGM) or actually heated enough to dry out (in the case of gel cell) leading to loss of that portion of the cell. With a flooded battery this doesn’t happen as easily because the electrolyte is mobile and can flow around if there is a hot spot.

  2. Thanks for sharing this William. This was on my list of future questions for you.

    All the best,

    Rob Lutz

  3. Which setting do you use? I would think the middle one for AGM, if the top one didn’t say Odyssey.

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