Strange battery issue

[wpoll]

Originally Posted by 80stech

... I didn't know there is different chargers for AGM though ??

A wet-cell lead-acid car battery has six cells, each of which has a typical resting voltage of 2.1 volts. Therefore, since the cells are connected in series, the total rest voltage of a fully charged battery should be at least 12.6 to 12.8 volts.

Things are a little different with AGM (Absorbent Glass Mat) batteries. The minimum rest voltage of an AGM battery is 12.8 volts. If this voltage drops down to 12.6 volts, the battery is only 75% charged. If it drops down to 12.3 volts, the battery is only 50% charged.

When an AGM battery’s resting voltage is at or below 11.80 volts, the battery is effectively flat.

Under normal conditions most 12-volt automatic battery chargers will work on an AGM battery, but the battery will only charge to about 80 percent of its full capacity. Many newer battery chargers have settings specifically for AGM batteries.

[80stech]

Charger voltage will be well above 12.8 volts (vehicle will be at least 13.8v) where both batteries are full using those numbers so I don't see how the AGM will only be at 80% ?? AGM is mostly a more efficient lead acid technology not really a different battery like lithium would be or am I missing something ?

[wpoll]

I can't talk the chemistry of it but lots of information states that AGM require different charging...

Stuff like this...

https://www.interstatebatteries.com/...an-agm-battery

(Not saying that this is entirely correct either!)

[80stech]

I 'think' that's saying the AGM is more susceptible to overcharging at higher voltages (and amps) (17v they say) so I can't see that being a big problem unless someone leaves a charger on for too long or maybe a maintainer with a high voltage which isn't good for a regular battery either. On the other hand you are saying that the AGM will only be at 80% with a regular charger ??
I'm going to check my chargers tomorrow, the newest I have is about 5 or 6 years old and I have only charged an AGM battery once in my lifetime so far!

[wpoll]

Originally Posted by 80stech

I 'think' that's saying the AGM is more susceptible to overcharging at higher voltages (and amps) (17v they say) so I can't see that being a big problem unless someone leaves a charger on for too long or maybe a maintainer with a high voltage which isn't good for a regular battery either. On the other hand you are saying that the AGM will only be at 80% with a regular charger ??
I'm going to check my chargers tomorrow, the newest I have is about 5 or 6 years old and I have only charged an AGM battery once in my lifetime so far!

I've seen other info. that indicates that the optimal charge profile for AGM is a little different than for wet cells, hence the inability to achieve a full charge with some standard chargers.

Lead-acid batteries reach about 80% of the total charge capacity via "bulk charge" and the remaining charge is achieved via "absorption charge". It's possible that some older charger types can fail to detect this charging stage point and therefore do not fully charge the AGM battery types.

This means that (in theory) a car's charging system would need to take AGM into account but I've run AGM batteries in older vehicles (like my BMW motorcycle) with zero issues. YMMV

[80stech]

I think 'maybe' the translation to 'old school' would be that the AGM has less 'surface charge' to fool the charger into thinking it's full ?
If you look at it from the other perspective it also is better at holding the voltage as it drains Definitely not straight forward though I guess.

If what you are saying is true then the AGM should be a much worse choice for the short trips??

@Clockwork---- did the BMW dealer say anything about switching over ??
Not saying that the dealer knows anything more but just curious?

[andrewwynn]

Originally Posted by wpoll

A wet-cell lead-acid car battery has six cells, each of which has a typical resting voltage of 2.1 volts. Therefore, since the cells are connected in series, the total rest voltage of a fully charged battery should be at least 12.6 to 12.8 volts.

Things are a little different with AGM (Absorbent Glass Mat) batteries. The minimum rest voltage of an AGM battery is 12.8 volts. If this voltage drops down to 12.6 volts, the battery is only 75% charged. If it drops down to 12.3 volts, the battery is only 50% charged.

When an AGM battery’s resting voltage is at or below 11.80 volts, the battery is effectively flat.

Under normal conditions most 12-volt automatic battery chargers will work on an AGM battery, but the battery will only charge to about 80 percent of its full capacity. Many newer battery chargers have settings specifically for AGM batteries.

I was more worried about an old timey charger over charging and damage AGM battery.

I ran this automatic charger overnight on my 90 Ah AGM that has been hovering around 60% SOC due to limited driving and BMW aiming for 80% max.



I was unaware of this possibility but now at least I know I can "mostly charge" my AGM without killing it using one of these battery chargers.

Regarding flooded vs. AGM my understanding is the AGM is better at dealing with low SOC without damage and more shaking/vibration.

When wife and I both had e53 I only put flooded in hers and AGM be mine as I'm much more rough on the car (off road, hard curves/stops etc). Also at sam's club under $200 for 90a AGM is not enough to say no to just in case it'll help with longevity.

I do want to get a proper AGM charger so when I'm not driving for long periods I can top off the battery not just to 80%.

[Clockwork]

So, I researched my C-Tek chargers and they have a specific AGM/cold weather charging/Storage mode on the 3300 and 7002 models, which just takes longer to fully charge a battery before maintenance/storage mode kicks in. So I'm safe

[workingonit]

Originally Posted by wpoll

A wet-cell lead-acid car battery has six cells, each of which has a typical resting voltage of 2.1 volts. Therefore, since the cells are connected in series, the total rest voltage of a fully charged battery should be at least 12.6 to 12.8 volts.

Things are a little different with AGM (Absorbent Glass Mat) batteries. The minimum rest voltage of an AGM battery is 12.8 volts. If this voltage drops down to 12.6 volts, the battery is only 75% charged. If it drops down to 12.3 volts, the battery is only 50% charged.

When an AGM battery’s resting voltage is at or below 11.80 volts, the battery is effectively flat.

Under normal conditions most 12-volt automatic battery chargers will work on an AGM battery, but the battery will only charge to about 80 percent of its full capacity. Many newer battery chargers have settings specifically for AGM batteries.

Originally Posted by andrewwynn

I was more worried about an old timey charger over charging and damage AGM battery.

I ran this automatic charger overnight on my 90 Ah AGM that has been hovering around 60% SOC due to limited driving and BMW aiming for 80% max.



I was unaware of this possibility but now at least I know I can "mostly charge" my AGM without killing it using one of these battery chargers.

Regarding flooded vs. AGM my understanding is the AGM is better at dealing with low SOC without damage and more shaking/vibration.

When wife and I both had e53 I only put flooded in hers and AGM be mine as I'm much more rough on the car (off road, hard curves/stops etc). Also at sam's club under $200 for 90a AGM is not enough to say no to just in case it'll help with longevity.

I do want to get a proper AGM charger so when I'm not driving for long periods I can top off the battery not just to 80%.

I use different types of chargers for my standard and AGM batteries, depending on the state of charge and length of charge time. I have

• 1) an AGM (Optima Yellowtop, 13 years old, in my camping trailer),
• 2) a Walmart Everstart 11 year old flooded-cell (in my '04 Chevy 2500HD),
• 3) an 8 year-old Duracell flooded-cell, from Sam's Club (in my '04 HHR Panel),
• 4) a 7.5 year-old O'Reilly SuperStart battery (in my '98 GMC 1500), and
• 5) a supposedly 6-year old battery in my X5 (I can't remember even the name or build date, and it's buried under tons of gear in the trunk)

All are always kept on a charger/maintainer whenever parked at home. My wife's '14 Lexus never is, and I should really pay more attention to it, but, I'm not allowed to drive it.

If the battery is near or at full charge (11.5-12.8v) then I'll use a "smart" (micro-processor-controlled) high-frequency pulsating-power Charger/Maintainer to desulphate and maintain both types of batteries (my C/M's are 1.25-2 amps), and are used fulltime, year-round, since some of my batteries are in vehicles (or a trailer) that sit for months between uses. Here are the charger/maintainers I use:

• 1) a 1.25A Battery Tender for my BMW X5 it's probably 8 years old now,
• 2) two Amazon Basics Battery 2A Chargers both are 3 y.o. for both my Chevy and GMC pickups,
• 3) an Autozone Duralast 1.5A charger 9 y.o, for my HHR Panel,
• 4) a Battery Minder Plus, 1A, 12 y.o., for the AGM battery in my trailer,
• 5) and a Black & Decker Bm3B 2A 11 y.o. charger as a backup (or, for the riding mower, formerly used on my wife's Cobalt, while it was being worked on for 3 years)

If the battery falls below 11.5v, then I'll use a combination of a newer lower-amperage (2-20 amps ) "smart" charger to recondition the battery, and an older "dumb" charger with higer amperage (20-40 amps) to shock the battery back to life, so to speak. I've done this on the AGM battery in my trailer twice, after I had let it die following longterm neglect (I thought the C/M was on but it was unplugged, and it was blocked by building materials in the garage...a problem since rectified). See this post for details:https://xoutpost.com/1238604-post17....oogle_vignette and this one for the chargers I have: https://xoutpost.com/bmw-sav-forums/...agnostics.html

I'll probably not get another AGM in the future, since the cost is more than a standard flooded-cell battery, and I don't go off-road or subject my batteries to other harsh conditions, anymore (ask me about my experience with "gel" drag-racing batteries). I've gotten long-lives from my batteries ever since I started maintaining them with "smart" charger/maintainers (a step above the old, "dumb" trickle-chargers of my youth), and can rely on them.

[Clockwork]

Originally Posted by workingonit

I'll probably not get another AGM in the future, since the cost is more than a standard flooded-cell battery, and I don't go off-road or subject my batteries to other harsh conditions, anymore (ask me about my experience with "gel" drag-racing batteries). I've gotten long-lives from my batteries ever since I started maintaining them with "smart" charger/maintainers (a step above the old, "dumb" trickle-chargers of my youth), and can rely on them.

I agree with your comment. I only went with an AGM this time because I wanted to see what the hype is about AND the BMW mech I go to ONLY sells OE AGMs now. SURE, I could have gone to Interstate or a local basttery seller to but an old school batt that is way cheaper and for the most part has done me well, 'specially since I have my vehicles on tenders almost 80% of time when at home (I mean why not, I have them...) so its BIT of an R&D for me.
I am happy to day that the first time I started my X5 yesterday after installing a fully charged AGM, that engine ROARED to life much bigger than over the last year. so perhaps its been a battery thats been slowly dying and the alternator has been limping it along. so nice to hear that N62 start so vigorously tho (and yes this could have happend regardless of battery type - I'm not praising an AGM for its starting power here)