Benefit to charging AGM battery to full capacity?

NatersXJ6

Explorer
Odyssey's recommended charging profiles are on page 15 here: https://www.odysseybattery.com/documents/US-ODY-TM.pdf
The bulk charge requirement is simply stated, but critical: "Note the charger current in the bulk charge mode must be 0.4C10 or more." (Page 16)
The minimum charge current for OPs 34R-1500 is 25A.
The absorption stage recommended is 14.7v for up to 8 hours.


The same page includes shows a cycle life graph which shows how the life is drastically reduced if the battery is undercharged.

My experience with replacing two Odyssey batteries after about 3-4 years each (at almost $300/pop) matches their published data. Believe me or don't. Believe Odyssey or don't. The good news is that a $4 voltmeter and proper test technique will tell you at the end of every weekend whether the battery got back to 100% SoC. Try it for a few trips and collect your own data. Or do what I did and after a couple of batteries decide that maybe $150 worth of charger for a $300 battery isn't a terrible investment.

Even buying the nice charger and running it almost every weekend I frequently drained and killed an OdysseyPC1500 T battery in my JK. Recognizing that I was running a full time fridge, a short commute, and live in a hot environment, I eventually decided that a $100 Group 27 FLA and frequent maintenance / replacement was a better plan than $150-200 per year in special order Odyssey replacements.
 

rayra

Expedition Leader
Even buying the nice charger and running it almost every weekend I frequently drained and killed an OdysseyPC1500 T battery in my JK. Recognizing that I was running a full time fridge, a short commute, and live in a hot environment, I eventually decided that a $100 Group 27 FLA and frequent maintenance / replacement was a better plan than $150-200 per year in special order Odyssey replacements.
where's that jeremiah Johnson nodding gif when I need it.

Making a virtue out of the vice of being poor, I went with dual 78s, at $90 each. I buy one every ~12-18mos, and bump the Starter to the Aux. Last round I bumped the Aux to my old C-10 sitting in the driveway. Next round I bump the Aux to commence building a home battery bank. I went matching so I could use both to power a winch, or if the starter battery crapped out I could swap to the Aux (but the way things are wired now I can just trigger the combiner solenoid and feed the vehicle. And I went with Interstate thru Costco. I can get a no fuss replacement in 550+ locations across CONUS and we're planning a lot of road trips late this summer if we ever get out of house arrest.
And I'm partially solving the deep drawdown issue with augmentation via rooftop solar and I just put a phat 200A++ alternator in my Suburban.

and speaking of that new high output chinese factory alternator replacement, it charges at 14.6-14.7, vs the factory Bosch's 14.1-14.2. So it very well could support an AGM battery.
Too, my Renogy PWM / rooftop solar backfeeds my Aux and it also charges at ~14.6 and is battery type selectable. So that would also solve the AGM/House recharge issue.
First couple weeks of the new ALT I was getting a whiff of battery vapors / ozone and got paranoid about overcharging, but after the first maintenance peek under the caps and a little distilled water added, have had no other signs or concerns.
 
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CaliMobber

Adventurer
One last note. Look into the big 3 mod. Essentially improveing the grounding of the factory setup whitch it pretty poor. You run a larger ground wire from battery to the frame, body and engine. I went overboard and ran 2 awg. I also ran 2 from the alternator to the battery bypasing the 8awg factory wire.

I gained about .5v in my charging and that seemed pretty normal from reading online reports. This is just removing the resistance in the wires preventing voltage drop in the charging system.
 

67cj5

Man On a Mission
My Alternator charges at around 14.7 to 14.8+, My starter battery is an 80Ah 800cca AGM, The vehicle is 2 years old and so is the Battery, Due to the lockdown I have been charging it about every 10 days, From the start of the lockdown I did not charge it for about 2 weeks,, I noticed that the voltage goes right up over 13v when it comes off the charger but it settles around 12.9+ and drops within a few minutes to around 12.8v,

I checked it 24 hours later and it is reading 12.254v, I thought that the battery might be stuffed but when the battery is reading 12.8v+ and I hook the battery up the voltage drops to around 12.5v +/- because I can hear buzzing and clicking as the vehicle sets it's self up,

I am charging the Battery using a NOCO G15000 / 15Ah Smart charger and while the battery is on Charge I am using the NOCO GB150 Boost to power the Vehicle while the battery is Charging,

The 15Ah Noco charges the battery right up in about 2 or 3 hours then it goes in to it's equalization mode for about 2 hours and when it stops pulsing it shuts off and then I disconnect it and hook the battery back up to the Car/Van,

I am not sure if the battery is stuffed or whether it is the parasitic drain that is making the voltage go all over the place,
 
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Joe917

Explorer
Disconnect the battery from the vehicle. Charge it with your NOCO. when it is charged leave it about 4 hours, it should be 12.7 V. Check it 24 hrs later it should still be 24 V.
 

67cj5

Man On a Mission
Disconnect the battery from the vehicle. Charge it with your NOCO. when it is charged leave it about 4 hours, it should be 12.7 V. Check it 24 hrs later it should still be 24 V.
Sorry do you mean 12v not 24v ?
 

67cj5

Man On a Mission
yes sorry , fat fingers, should still hold 12.7 V
Cool, Thanks for that,

I hooked power through the OBD Port and took the positive lead off the battery and I have hooked up the Noco 15Ah Charger and it ran through it's stages in under 10 minutes and then it went in to the equalization mode where it fires pulses in to the battery until it has done it's thing so I will check it in about 2 hours and see if it has done,

I am powering the OBD port using the Noco OBD Lead with it plugged in to the Dometic PLB-40 because the Noco GB150 Booster can do it but they shut down after 7 hours and I don't want to have to get the Van reprogrammed so I thought it was best to keep it powered up with something that is not on a Timer,

So fingers crossed the Battery will still be ok in the morning in about 13 hours time, (y)
 

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