AGM won't fully charge from alternator?

[BrendanC]

my aftermarket 370 amp alternator upon cold start is at 15 volts that tapers down to 14.8 when hot. my last set of everstart max group 78 FLA’s went 5 years like this. i put a set of diehard platinum group 34 AGMS in last year and so far so good. starter still sounds like it’s going to explode when i hit the key.

 

[ripcord]

my aftermarket 370 amp alternator upon cold start is at 15 volts that tapers down to 14.8 when hot. my last set of everstart max group 78 FLA’s went 5 years like this. i put a set of diehard platinum group 34 AGMS in last year and so far so good. starter still sounds like it’s going to explode when i hit the key.

The alternator in my Ford truck is exactly the same, though I think the regulator may be getting weak as it used to tapper from 14.6v down to 14.3v. I'm not worried, though, as the truck is mostly short tripped anyway.

 

[CKN]

My Ford has a parasitic draw in my console shifter sensor (I'm 99% sure that's where it is) but if I engage PARK rather forcefully the battery stays charged. 2-3 times last year mine drew down overnight. One night I camped out in my truck (last fall) and noticed that the cluster only went super dim, it didn't shut all the way off. I slammed doors, I popped the hood, I checked the console and glove box light - nothing. I finally decided that I'd drive it a bit to top it up as I was only going to rack out about 4 hours and when I parked it again the cluster went right off. I was hot until I delved into it a bit.

My girls Navigator is so stupid loaded that her battery draws down in about 3 days. The more electronics with Keep Alive, the faster it drains. And it's all normal.

My 2020 F150 Lariat has a factory interior/exterior alarm that's always on. In addition to whatever else draws from the battery when the truck is turned off. However-the vehicle is also supposed to adjust what it draws as the battery discharges.

 

[JHZR2]

Normal at idle for some of the Nissan smart charging systems.

That’s fine but it’s dissociated from the OP regarding AGM. No battery, flooded or AGM will be properly charged when the voltage is regulated to such levels. Frankly it’s abusive for both, and life will be affected. And, OP implied that any smart charging capabilities were disabled.

I’m not sure why folks buy AGM without a real need. Sure, they self discharge less, are better sealed, and recombine hydrogen and oxygen better. But they aren’t a panacea for anything.

 

[4WD]

my aftermarket 370 amp alternator upon cold start is at 15 volts that tapers down to 14.8 when hot. my last set of everstart max group 78 FLA’s went 5 years like this. i put a set of diehard platinum group 34 AGMS in last year and so far so good. starter still sounds like it’s going to explode when i hit the key.

Mechman that’s over 5 years old ?

 

[Snuckster]

As mentioned in my OP, my smart charger is defeated - by me - common mod on these and its really not all that "smart" truthfully. Its running completely off the alternators internal voltage regulator old school - has been for years.

The charge voltage varies between 14.2 and 13.2V while driving.

I have seen inconsistent results from people bypassing the sensor on stock setups. Usually puts voltage at 13.8 at the battery which is not enough to keep any battery truly charged.

my 05' Xterra uses the same smart charging system.
using 100% stock wiring (nothing grounded directly to the battery) the charging system runs in traditional mode pegged at 14.2-14.4v by turning on the AC
if it wasn't pouring rain right now id take a video to prove it

when not running the AC the system goes with its ECO algorithm that runs everything off the battery (no charging) taking it down to somewhere around 80-90% state of charge in best case scenarios. I noticed with my 04' Armada that it worked well when you had a lot of stop n go type city driving because it would put out 15v when coasting or braking) but after a particularly long freeway run travelling uphill it actually drained enough of the battery to require my little jump pack after stopping for treats on the way home. After I figured out what was happening I didn't have an issue ever again.

I keep a 20w solar panel suction cupped to my windshield running through a cheap PWM plugged into the constant on 12v accessory outlet on the dash when I know its going to be parked for a bit just in case. keeps everything topped off and I don't have to fuss with asking neighbor if I could run my extension cord to their patio lol

 

[BrendanC]

Mechman that’s over 5 years old ?

JS alternators. dad has a 400amp mechman that when warm holds 14.2 or so. this JS has been rock solid through many houston summers. with AC on at idle i clamp at 110-120amps just running the E fans and the truck.

 

[UncleDave]

Alternators rarely to never fully charge AGM's, or even wet leads.

My Titan never fully charged my Odyssey, but its lasted 15 years and still going.

Rather than go down a " mod the car road" If you can plug it at home a high quality maintainer charger and a 2.00 lead with a quick connect plugged in every night or even semi regularly will keep you humming for a decade.

 

[SC Maintenance]

I have seen inconsistent results from people bypassing the sensor on stock setups. Usually puts voltage at 13.8 at the battery which is not enough to keep any battery truly charged.

my 05' Xterra uses the same smart charging system.
using 100% stock wiring (nothing grounded directly to the battery) the charging system runs in traditional mode pegged at 14.2-14.4v by turning on the AC
if it wasn't pouring rain right now id take a video to prove it

when not running the AC the system goes with its ECO algorithm that runs everything off the battery (no charging) taking it down to somewhere around 80-90% state of charge in best case scenarios. I noticed with my 04' Armada that it worked well when you had a lot of stop n go type city driving because it would put out 15v when coasting or braking) but after a particularly long freeway run travelling uphill it actually drained enough of the battery to require my little jump pack after stopping for treats on the way home. After I figured out what was happening I didn't have an issue ever again.

I keep a 20w solar panel suction cupped to my windshield running through a cheap PWM plugged into the constant on 12v accessory outlet on the dash when I know its going to be parked for a bit just in case. keeps everything topped off and I don't have to fuss with asking neighbor if I could run my extension cord to their patio lol

The "smart" charging is a single wire that can only lower the charge rate - not increase it. Without the smart charger enabled on my lead acid batteries it kept them at a higher state of charge as measured by a battery tester.

I think what your observing is the alternator charging higher due to the battery being more discharged with the smart charge system on. I have studied the FSM description of the system, the schematic, and actually had an old alternator apart - there is no ability i can find for the ECM to increase the voltage.

I could plug it back in but I don't think it will help. Maybe I will for fun.

Mine will charge at 14.2V for an extended period without the smart charger if the battery is discharged. My radar detector displays the system voltage in real time all the time, and peak voltages for me have never changed, with or without the system. Min voltages have.

This is the FSM smart charge troubleshooting description. There is a 0.5V voltage increase between a 40% and 80% duty cycle call for charge. Possibly other Nissan systems are more advanced, this one isn't.

“BATTERY VOLT” 2 seconds after setting the DUTY value of “ALTERNATOR DUTY” to 40.0 %

: 12 - 13.6 V
“BATTERY VOLT”

20 seconds after setting the DUTY value of “ALTERNATOR DUTY” to 80.0 %

: +0.5 V or more against
the value of “BATTERY
VOLT” monitor when
DUTY value is 40.0 %

 

[SC Maintenance]

I’m not sure why folks buy AGM without a real need. Sure, they self discharge less, are better sealed, and recombine hydrogen and oxygen better. But they aren’t a panacea for anything.

I specifically bought lead acid for the cars my wife and daughters drive since I didn't need any drama in those. For this one, it was only a couple bucks more and has 1 year longer warranty. Many of the Nissan guys online have run AGM for a long time so I figured it was a good chance to try one. I have never had a battery last more than 4 years before it got too weak for my liking. Don't know if its vibration or Southern heat. I do plug them into charger about once a month minimum and haver for years, so I don't think that is it.

 

[SC Maintenance]

OK, so some more diagnostic data.

After I tested it yesterday, I put my 1A Noco trickle charger on it, expecting it to take a while. I went out to check on it before bed a couple hours later and the light already went green - so Noco didn't think it was very discharged - by definition 2Ah at most? Seems odd.

I let it sit overnight and tested it again this morning - still a bit of overvoltage on it - 12.65V. I decided to go ahead with a draw test anyway even though there was no signs. Within 30 minutes it was at about 15mA and holding. So its drawing nothing when off.

Didn't drive it today. Just now I tested again. 12.55V, more CCA than rated, 95% charged, resistance at 3 milliohm's. So the battery looks good now.

I guess I will run it some more and check again. Maybe the factory charge setup just can't get it all the way there, coupled with a cheap Clarios battery and a imprecise battery tester, combined with my OCD and the perception of a problem?

 

[LenZee]

OK, so some more diagnostic data.

After I tested it yesterday, I put my 1A Noco trickle charger on it, expecting it to take a while. I went out to check on it before bed a couple hours later and the light already went green - so Noco didn't think it was very discharged - by definition 2Ah at most? Seems odd.

I let it sit overnight and tested it again this morning - still a bit of overvoltage on it - 12.65V. I decided to go ahead with a draw test anyway even though there was no signs. Within 30 minutes it was at about 15mA and holding. So its drawing nothing when off.

Didn't drive it today. Just now I tested again. 12.55V, more CCA than rated, 95% charged, resistance at 3 milliohm's. So the battery looks good now.

I guess I will run it some more and check again. Maybe the factory charge setup just can't get it all the way there, coupled with a cheap Clarios battery and a imprecise battery tester, combined with my OCD and the perception of a problem?

I've had good results in both my vehicles that aren't AGM optimized. Lasted longer than warranty and in the case of my van I replaced it due to age, Still cranked fine (8yrs)

 

[meep]

Wow, thanks for letting us know your MPG experience. I had no idea it could be so significant.

I came across a post a while back from an engineer who contributed to writing the owners manuals for Ford during that time. He said the BMS fuel efficiency savings were more than auto-stop/start. Pretty wild.

 

[SubLGT]

My new Walmart Everstart Platinum AGM (manufactured in S. Korea by Hankook) got up to 12.78V (at 60F) after I got it home and charged it at 7A.. After running it through a "formatting" procedure, it now sits at 12.98V (OCV at 60F) 48 hours after charging.

 

[GMBoy]

You should have purchased the correct spec lead acid battery. Vehicles spec'd for AGM have charging systems geared for charging an AGM battery and it's not recommend to run a lead acid in an AGM spec system and vice versa.

 

[JHZR2]

OK, so some more diagnostic data.

After I tested it yesterday, I put my 1A Noco trickle charger on it, expecting it to take a while. I went out to check on it before bed a couple hours later and the light already went green - so Noco didn't think it was very discharged - by definition 2Ah at most? Seems odd.

I let it sit overnight and tested it again this morning - still a bit of overvoltage on it - 12.65V. I decided to go ahead with a draw test anyway even though there was no signs. Within 30 minutes it was at about 15mA and holding. So its drawing nothing when off.

Didn't drive it today. Just now I tested again. 12.55V, more CCA than rated, 95% charged, resistance at 3 milliohm's. So the battery looks good now.

I guess I will run it some more and check again. Maybe the factory charge setup just can't get it all the way there, coupled with a cheap Clarios battery and an imprecise battery tester, combined with my OCD and the perception of a problem?

Unless you’re taking data and plotting it to verify, I suspect your parasitic test isn’t accurate. Some module is probably waking up and then sleeping again.

 

[ripcord]

Parasitic draw tests can be done the hard way, too. Fully charge it and let it set in the vehicle for 48 hours and check the voltage. Then take it out of the vehicle, charge it and let it rest for 48 hours. If the voltage is significantly different, then there is a parasitic draw.

 

[SC Maintenance]

So 36 hours since charge, vehicle not run, back to where I started - 12.45V, 81% SOC on the tester. Vehicle has not been run. So I am not crazy.

Unless you’re taking data and plotting it to verify, I suspect your parasitic test isn’t accurate. Some module is probably waking up and then sleeping again.

I really can't see this. Even if that was true - it showed no sign of drawing down my 4 year old lead acid battery, and even when this very simple system "wakes up" - the entire control system only pulls about 200mA for maybe a minute and then drops to 80mA, then down to 15mA in just a few minutes. I don't know - this sounds remote to me but I suppose anything is possible.

I still have the old lead acid battery. I charged it when I took it out just because, and its still holding 12.65 V - its just got about half its rated CA hence the reason I replaced. I could stick it back in and see what it does anything different than before - but when it was in - which was less than 2 weeks ago, it would hold a charge better than this AGM.

I think the AGM is just not good. Of course I bought it, I own it.

Cost of a good AGM education may become $200 and some of my time. I'll make sure my Gooloo jump pack is well charged.

 

[SC Maintenance]

After running it through a "formatting" procedure,

Can you explain this to me?

 

[LenZee]

You should have purchased the correct spec lead acid battery. Vehicles spec'd for AGM have charging systems geared for charging an AGM battery and it's not recommend to run a lead acid in an AGM spec system and vice versa.

I've had the longest lasting batteries in a lead acid charging vehicle using AGM battery. Probably worse for lead acid battery in AGM charging system though.