Losing my patience with AGM batteries

Not sure what's going on but the last two AGM batteries I have had in my truck keep screwing me when its cold out. I had an odyssey AGM that stopped holding a charge after about 3 to 4 years then I bought an Interstate dual purpose AGM battery that has been great for about a year now but all of a sudden when it gets cold out it won't hold a charge.

When it snowed a few inches a couple weeks back the truck wouldn't start so I through on the odyssey battery charger I bought to try and reconditioned my old odyssey battery. I left the charger on over night and the truck started no problem and has been fine since. Now we get another snow event and cold weather and the truck won't start again. I don't have crazy accessories, only my winch that's hooked up full time. I do have a 12v plug and an Anderson plug in the back but nothings plugged in. I don't think I have a parasitic voltage loss.

Again it only seems to be an issue when its cold out. Does anyone one else have issues with AGM batteries?

Ray,
I've had issues if I didn't get them charged to a high enough voltage, short life and bad surprises. On the other hand, since I boosted my charge voltage I'm 4 years in on a pair of optima's and they seem solid still. 11/2016 I added a 2nd battery set-up and made a voltage booster for +0.5V and usually see 13.8-14.9V on the scangauge now. Check out Odysseys specs against whatever your alternator has been putting out, could be a place to start.

Happy Thanksgiving!

AimCOTaco said:

Ray,
I've had issues if I didn't get them charged to a high enough voltage, short life and bad surprises. On the other hand, since I boosted my charge voltage I'm 4 years in on a pair of optima's and they seem solid still. 11/2016 I added a 2nd battery set-up and made a voltage booster for +0.5V and usually see 13.8-14.9V on the scangauge now. Check out Odysseys specs against whatever your alternator has been putting out, could be a place to start.

Happy Thanksgiving!

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This is exactly what I was typing when you posted it. Just toss on a diode setup and it will likely fix the issue. I wasn't getting 100% charge before I put in a diode setup. I am presently boosting by 0.4v. Odyssey says it will charge to 100% with charge voltages as low as 14.4, but that wasn't my finding.

Here is the Odyssey pamphlet on the AGM extreme batteries. See the chart on page 14 about the numbers of charge cycle based on the charge voltage. I took a screenshot to post. It starts at the bottom of column 1 with "Effect of undercharge in cycling applications" and continues through into column 2. It also discusses preferred charge voltages.

Odyssey are the most sensitive in my experience about a rigorous charging routine. I have two of them. I personally use three methods to charge them. One is a voltage-bump on my alternator to 14.8V, an Iota DLS-45 with an IQ4-AGM controller and a Morningstar SS-15L solar controller. I use a temperature compensated profile from the technical manual @gungriffin links (e.g. adjusted at 24mV/°C). Even with this they seem to age faster than Northstar AGMs (such as the X2 from Battery Plus).

My recommendation when asked (which is rare) is the only reason to really spend money on AGM is if you need them for unusual mounting on their side or inside where minimally venting is a benefit. Mostly they aren't worth the extra money IMO. You're better off financially using standard name brand flooded types. They last 75% as long (and often just as long if you follow poor charging and conditioning) at 50% the price.

gungriffin said:

This is exactly what I was typing when you posted it. Just toss on a diode setup and it will likely fix the issue. I wasn't getting 100% charge before I put in a diode setup. I am presently boosting by 0.4v. Odyssey says it will charge to 100% with charge voltages as low as 14.4, but that wasn't my finding.

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Thanks for the tip but electricity is like algebra for me. Where would I install the diode at?

DaveInDenver said:

Odyssey are the most sensitive in my experience about a rigorous charging routine. I have two of them. I personally use three methods to charge them. One is a voltage-bump on my alternator to 14.8V, an Iota DLS-45 with an IQ4-AGM controller and a Morningstar SS-15L solar controller. I use a temperature compensated profile from the technical manual @gungriffin links (e.g. adjusted at 24mV/°C). Even with this they seem to age faster than Northstar AGMs (such as the X2 from Battery Plus).

My recommendation when asked (which is rare) is the only reason to really spend money on AGM is if you need them for unusual mounting on their side or inside where minimally venting is a benefit. Mostly they aren't worth the extra money IMO.

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The only reason I bought this specific model was because its a dual purpose battery, both deep cycle and starting. I don't want to have to go the route of a dual battery set up if i don't have to. I have a few plug-ins in the back for my fridge and a light. I have those wired directly to the battery using the two small post on top of the battery.

RayRay27 said:

Thanks for the tip but electricity is like algebra for me. Where would I install the diode at?

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@bassguyry would you be able to offer any insight on where you got the parts to do this?

He just built out the diode that goes in the voltage sensor fuse for his 100 series. I would imagine it is much the same for the 80 series.

So I had the alternator/battery tested today and both the battery and the alternator passed but it said my diode test failed. Do I need to replace my alternator now? I can't exactly pull my alternator and have it tested.

RayRay27 said:

So I had the alternator/battery tested today and both the battery and the alternator passed but it said my diode test failed. Do I need to replace my alternator now? I can't exactly pull my alternator and have it tested.

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Did you put a voltmeter on the battery terminals with the truck running to figure out what your alternator is putting out? Maybe that’s obvious, I’m not hip with electrical either... I do have pretty good battery/alternator testers that you can borrow for troubleshooting, sounds like you had to go somewhere to perform a test. I’m down to having one tester but if I can find one of the two I’ve lost than you can have one! Come to think of it, I probably didn’t lose em, just forgot who borrowed them lol

DanielChase said:

Did you put a voltmeter on the battery terminals with the truck running to figure out what your alternator is putting out? Maybe that’s obvious, I’m not hip with electrical either... I do have pretty good battery/alternator testers that you can borrow for troubleshooting, sounds like you had to go somewhere to perform a test. I’m down to having one tester but if I can find one of the two I’ve lost than you can have one! Come to think of it, I probably didn’t lose em, just forgot who borrowed them lol

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I haven't done a voltmeter test yet. I just had it tested at autozone since I was there dropping off some used oil.

gungriffin said:

@bassguyry would you be able to offer any insight on where you got the parts to do this?

He just built out the diode that goes in the voltage sensor fuse for his 100 series. I would imagine it is much the same for the 80 series.

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I bought everything on Amazon. A whopping $10 in parts. I still have leftovers, so I'm happy to whip one up for you @RayRay27 - just let me know. Takes all of five minutes to solder together.

I'd like to do this for my 80 also!

bassguyry said:

I bought everything on Amazon. A whopping $10 in parts. I still have leftovers, so I'm happy to whip one up for you @RayRay27 - just let me know. Takes all of five minutes to solder together.

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Man thats super awesome of you to do that! Again I'm not a electricity guy so I'm still a little fuzzy on the adding a diode process and where it goes?

RayRay27 said:

Man thats super awesome of you to do that! Again I'm not a electricity guy so I'm still a little fuzzy on the adding a diode process and where it goes?

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No sweat, mi amigo! It's super easy. I just put one together for you - let me know if you want to meet up, or I'm happy to just drop it in the mail (PM me your address, if so).

I followed @AimCOTaco's instructions in this thread (see post #23) over at Mud. I took out the ALT-S fuse (7.5A, I believe) and replaced it with an "add-a-fuse" that has a diode in series (see pics of the one I just built for you below - the second pic just has some electrical tape added to the side). You'll just plug the actual ALT-S fuse into the add-a-fuse slot (where the blue 15A fuse is located in the pics below - the 15A fuse is just for display purposes only).

After adding the diode, I average anywhere between 14.1V and 14.8V while driving, though my voltage dips down to 13.4-13.8V under load at idle. Of course, this was after replacing my alternator...twice (had a brand new Denso go dead on me the first go-round).

I'm not familiar with 80s, so I'm not exactly sure if the voltage booster will work the same way as it does on my 100. Thus, my standard disclaimer applies: I'm not to blame if this mod results in any damage, sets your truck on fire, gives birth to baby unicorns (unless said unicorns consist of some minty fresh 40s, in which case, I get one for free ) - you accept all liability.

I'm going to have to figure this out as well. I'm having the same exact issues with my AGM batteries in my 80. I'll check my charging voltage and see where I'm at. Thanks for this thread!!!

LARGEONE said:

I'm going to have to figure this out as well. I'm having the same exact issues with my AGM batteries in my 80. I'll check my charging voltage and see where I'm at. Thanks for this thread!!!

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@LARGEONE - I've got one last diode if you want me to put together a voltage booster for you. Ray is picking one up from me on Saturday. Just let me know.

I would definitely take one! If you have time. Would also love to understand more about how this works? I am another electrical midget!

LARGEONE said:

I would definitely take one! If you have time. Would also love to understand more about how this works? I am another electrical midget!

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Gotcha, just whipped another one up for you. PM me and let me know if you'd like to pick it up, or I can throw it in the mail. The disclaimer I gave Ray applies here as well - it's not my fault if your truck catches on fire from using this thing.

Based on my admittedly limited understanding, adding a rectifier diode in series with the ALT-S fuse causes a voltage drop, which in turn results in the alternator increasing its output voltage (roughly 0.5V in this case). This helps achieve a greater charging voltage for the battery, which AGM batteries seem to need. Since adding mine, I've been consistently seeing a charging voltage of 14.1V-14.8V, as opposed to the 13.6V-14.1V before I installed the diode.

It's important to know the direction of the diode in this trick is critical. You want the forward voltage drop added to the circuit. Backward will trick the alternator into thinking there's no sense voltage and not regulate at all.

I make this point because not every truck's fuse box is identical and if you build a gadget using one of the Tap-A-Fuse blocks using a visual reference from the Interwebz it's possible to have things oriented wrong or not fit. By turning it around like this I was able to leave a nice length loop on the wire for strain relief rather than trying to cut the plastic and re-seal everything.

For example on a 2nd gen Tacoma the Alt-S location required a different arrangement to fit against the side and for the lid to fit back on.

This was also a Schottky I tried in an experiment, which gave less voltage bump (about 0.3V) because in the summer having too high of a voltage is just as damaging as too low. A junk box 1N4001 was pushing up against 15V on my truck and holding that for hours on the Interstate in August can cause venting. That's very bad to do on an AGM since there's no way to put the magic juice back inside unlike traditional flooded types where you can add back water if you boil it. An AGM (or maintenance-free for that matter) will vent if you push them too hard to prevent over pressure and if it does that's a one-way turn down Ruined Street.





In the end, though, I just ended up using a diode fuse from a Ford truck. The one I got was about 0.5V drop and works for my purposes almost year-round and fits inside the fuse box much cleaner. I just put the hobbled one in during long road trips in the summer now.