The LX 570 is equipped with an AGM battery

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yeLwWm

yeLwWm

Joined
Feb 5, 2024
Threads
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Location
Texas
This Duralast Platinum 24F-AGM battery has been in use for a year. I recently returned from a highway trip and tested the battery, only to find the charge was very low, which was strange.

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It turned out that AGM batteries require a higher charging voltage, so I spent $4 on a diode (Littelfuse 1 Amp Mini Diode - 02400113XP), cut the edge a little bit to insert.

The voltage increased from 14.01V to 14.47V at engine idle.

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What year is your LX? That mod won't work on the face lift LC/LX's unfortunately.
 
This is kind of the problem with AGM batteries on our 200 Series platform: the electronics aren't designed for it. You can trick it with a diode, but it's going to put stress on your alternator.
 
And clean up the terminals. I can’t tell for sure from the photo, but it looks like corrosion/rust on the positive terminal and it does not look like OEM? The connection between the posts and clamps should be shiny-bright. That may be part of the charging problem?
 
This is exactly why AGMs are not recommended for this platform.

After a year of systemic undercharging, causing internal sulfation, this battery is likely already very weak, with low reserves, and close to failure.

Solving the voltage issue with a diode is not a fix either.

If you live in a warmer environment and do longer trips in low speed traffic, rock crawling, or lots of idling, AGM batteries will overheat as under hood will easily get to 165*F +. Combine that with boosted voltage and AGM batteries, also known as VRLA (Valve Regulated Lead Acid) will gas off and fail.

AGMs are all around a liability to adventure travel in the 200-series because of the above incompatibilities. Which kind of defeats the point as that's what they are advertised to make better.
 
After driving for 40 minutes, the battery level returned to a fairly good level, indicating that the diode's voltage boost to the alternator was effective, even if it was only 0.4V. I hope I haven't lost too much battery health over the past year. Next time, I might switch back to a non-AGM battery if this AGM battery doesn't provide a significantly longer lifespan.

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@yeLwWm I can’t predict the future but it’s very possible you’re in better shape than others suggest. I’ve had two 200s (pre 2016) with AGMs and have gotten what I would call sufficient life out of them, 7.5 years +. Anecdote one - X2 Power Group 31 installed in early 2017, diode wasn’t installed until Feb 2019, and it is still trucking with the new owner nearly 9 years later. Truck lived in Northeast and Mid-Atlantic/South. Anecdote two - Northstar Group 31 installed 10/2017 and it finally gave up the ghost in July 2025 just short of 8 years old. Diode installed nearly, if not the entire, time. It still started the truck and I didn’t suspect any issues until my HVAC started intermittently resetting on start up. This truck lived in the Deep South and Southeast, went long periods without use.

Now did I switch my battery back to a FLA? Yup, sure did after I removed the diode. I don’t have any particular unique need for an AGM and assuming I get 4ish years out of a FLA, it is seemingly a zero sum game in terms of cost.

I would not run an AGM without a replacement or modified ALT S fuse for the reasons noted above. And none of this applies to 2016+ as I have zero experience with the later alternator/OE BMS.
 
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