Battery upgrade: from Lead/Acid to AGM

[Jay-Jay]

Hi everybody,
I was thinking about replacing my classic lead/acid battery with an AGM battery.
I know AGM batteries need a charge voltage of about 14,5V.
I monitored the voltage of my alternator. In the first minutes after start-up it stays between 14,3 and 13,9V. After 10 or more minutes of driving, as soon as engine bay temperatures get higher, voltage drops at about 13,4-13,7V.
Do you know if I can install an AGM battery anyway, without worrying too much or if it should be mandatory to replace the alternator with a different one specific for AGM batteries?
In the second case, what alternator do you reccomend for my engine (CBZB)?

[2226]

You will be fine. Those voltages are not set in stone. Charge range is 14.2-14.4V, float charge is 13.something to maybe 13.7V which is all fine.
It's still lead battery so won't have problems.

[Jay-Jay]

My concern regards the lifespan of an AGM battery which would be almost always charged under 14V, so it might never be fully charged.
Will this shorten its life and make it even shorter than a lead/acid battery?

[2226]

No, I doubt that. They're still lead acid batteries, but with benefits compared to the common flooded type.
I'd rather stick to them being slightly undercharged just in case you overcharge which causes more problems compared to the flooded type. Thermal runaway kinda stuff.
The car's charge voltage range should be more than adequate for your AGM.

[RUM4MO]

Remember, these AGM batteries that you are likely to fit to a car that came from the factory with a basic flooded lead acid battery, are really just "drop in" replacements for a basic flooded battery, but can be expected to last a lot longer.

My wife's car is a 2015 VW Polo 1.2TSI 110PS, so it came with "smart" charging, ie energy recovery during braking, it left the factory with an EFB which is a more rugged/robust version of a basic flooded lead acid battery with the advantage that it will tolerate being left at a lower charge level while being able to be "hit" with heavy charging during braking period - to avoid wasting energy, that type of battery can survive being used with a stop/start car, ie more tolerant to extra engine starts. I plan to replace it with an AGM battery, but so far, at almost 9 years old and 50,000miles, that battery refuses to die or even reduce its ability to store energy, which is annoying as I've already bought its next AGM battery! As that car has smart charging, I will be recoding the battery system to make the most out of that AGM battery when it needs to get fitted.

[Jay-Jay]

As far as I know cars factory equipped with a EFB battery have an alternator charge voltage which is very similar to what an AGM battery needs as well.
My friend's Polo 6C 1.2 TSI 90hp has about 14,7V of charge while driving in the city.
Unfortunately my car doesn't have Start&Stop nor an energy management control unit. So I can't code it for a different battery's technology.

No, I doubt that. They're still lead acid batteries, but with benefits compared to the common flooded type.
I'd rather stick to them being slightly undercharged just in case you overcharge which causes more problems compared to the flooded type. Thermal runaway kinda stuff.
The car's charge voltage range should be more than adequate for your AGM.

I really want to upgrade to AGM battery. Since I had my car, I replaced the battery 4 times. Each battery never lasted more than 3,5 years.
I also installed bigger batteries thinking they could last more, but I had almost no benefits.
At the moment the one installed on my car (Varta 74Ah) is already giving my signs of death after about 3,5 years.
I am tired of this.
My mum's old Audi A1 bought in 2011 had an AGM battery and we sold that car in 2021 still with that battery perfectly running. The new owner still has never replaced it at today.
At the moment I would like to install a 50ah AGM battery which has a smaller size than what is installed at the moment in my car, which will free up some space in the engine bay for some future engine mods I am planning.

Coming back to my concern about proper charge voltage: I did some online research and I saw a lot of people install diodes to make alternator charge voltage raise to AGM proper charge levels.
Will this cheap solution be possible on my car?
Everybody puts one or more diodes on the alternator's sense wire. The diode trick the tension's regulator making it read tension is lower than it really is, so the regulator raises the voltage output by an equal amount of what it thinks is missing.
Different type and number of diodes can give different results depending on the specific needs.
In my case a boost of just 0,5V might be enough to stay in a safe range.
What do you think?

[Tinman]

My orignal car EXIDE EFB battery for CHZC engine finally died after 8 years of used yesterday without warning, took eight try to start car and need to run car every few hours if i want to start car first try. Ive decided on BOSCH AGM same specification as the EXIDE EFB as replacement, brought from
Tayna.

[2226]

What do you think?

I think you're over-thinking it.
I'd just fit the AGM and go with it.

And yes, I'm tired of these batteries dying as well. On my 3rd since I bought the car in 2019.
One day it started up perfectly, I drove to work, parked it and when I came back later in the day it was completely dead. Turns out the network signal at the office is very bad and the tracker unit uses more energy. I have that with my mobile phone as well at the office. Battery does not last there.

In my mk1 Golf (2006 model) I think I changed the battery twice in 14 years of ownership. And that does not include the life it had before I got it.

Also, if you're feeling rich...
https://www.antigravitybatteries-uk.co.uk/

[RUM4MO]

One, hopefully, final comment on this topic, because I was not using my 2011 Audi S4 for much - only use it for long journeys, I bought a suitable CTEK charger/tester/maintenance unit, started using it in the "AGM" mode, obviously I didn't read the instructions properly, possibly after buying another one, just charger/maintenance unit this time, for my wife's 2015 VW Polo as it was also not used much during the first Covid lockdown, I must have read the instructions properly, it turns out that for "normal batteries" ie basic flooded, EFB and drop in AGM, the nonAGM charging mode is the correct one. The AGM mode is for special versions of AGM.

Maybe that gives you a bit more confidence that fitting an AGM in place of a basic flooded battery to a car with a basic "not smart" charging system, will be okay.

[ciclo]

Also, if you're feeling rich...
https://www.antigravitybatteries-uk.co.uk/

My brother-in-law bought a super ultra cheap white label (non-branded) battery for his BMW 520d at a well-known mall 14 years ago and it still works!
Knowing my brother-in-law, he probably got it with discount coupons that malls give away for upcoming purchases or things like that that I don't understand..., it is something exceptional and surprising because the car sleeps outdoors and makes really short trips, he is a truck driver and barely has time to take care of the car.
We gave this battery a slow charge last year because it seems to be showing signs of exhaustion, and he is sad and worried because he believes that he will never find a better battery again.
I'm going to send him your link telling him that those are the only batteries that he can currently install in his BMW 520d , ... to know what he thinks about it.

---

3.5 years is a short time for the life of a battery, it depends on how the car is used or 'sometimes' it also depends on the retrofitted 'improvements'.

[Jay-Jay]

I think you're over-thinking it.
I'd just fit the AGM and go with it.
[...]

[...]
Maybe that gives you a bit more confidence that fitting an AGM in place of a basic flooded battery to a car with a basic "not smart" charging system, will be okay.

Thank you, guys! Now I definetely feel more confident to install an AGM battery without worrying too much.

[...]
3.5 years is a short time for the life of a battery, it depends on how the car is used or 'sometimes' it also depends on the retrofitted 'improvements'.

You're absolutely right! My dad's A3 8L bought in 1999 needs a battery replacement every 6-7 years.
Instead, my Polo has always had this "short-life battery" problem since I bought it and even before doing any mods to it. I bought it when it was 3 years second hand. After 6 months I got stuck in the middle of a street and I had to push the car to make it start up.
I replaced the original 44Ah battery with a Varta Blue Dynamic battery of the same capacity, but it lasted only a bit more than 1 year.
Then I decided to put a bigger capacity battery: I went for an Akuma 80Ah (made by FIAMM), which lasted 3,5 years. It abandoned me at a gas station while I was about to leave the city for a short trip over the weekend. I had to push the car to make the engine start up and immediately turn around and go back to Rome and cancel the short trip, because I had no possibilities to immediately buy a new battery, replace it and continue with the short trip.
So I replaced it with the actual Varta 74Ah, bought it in December 2020, which is now 3 years and 7 months old.
Last sunday, I had to play with ODIS for about 30 minutes (all lights and radio were off) and the battery voltage went under 10V. Luckily I immediately connected my battery charger and left it do its work for more than 12 hours and it was able to fully recharge the battery.
Maybe all is fine, but all my previous experiences lead me to fear a battery replacement is near.

I use my Polo as a daily car, essentially for going back forth from home to the office and vice versa and during the weekend for some driving in Rome and short trips out of town.
On Monday-Friday I drive 40km per day, 20km straight per trip, which leads to about 1 hour of driving stuck in crazy traffic at peak hours. This kind of condition should allow the alternator to enoughly charge the battery.
Yet the batteries have never lasted much...
The Varta 74Ah battery installed at the moment is the first battery that is lasting a bit more.
I even brought my car to a car electrician who checked the alternator and for any unwanted dispersion and absorbtion, but all seems within factory specs.
I really hope an AGM battery could last more.
I think I will go for the Yuasa YBX9012 50Ah/520A(EN1).

[2226]

I'm hoping at some point to get a decent lithium battery jump pack to keep in the car for emergencies.
You might want to look for something like that and just keep it in the boot/trunk.
Good lithium packs can hold their charge for quite a long time due to low internal resistance and therefore very low self-discharge.

[Jay-Jay]

A friend of mine who studied electronical engineering told me about super capacitors to use in pair with a very small capacity lithium battery (20Ah) just for all the auxiliary services.
He says super capacitors have a huge crank power (more than 1000A). He offered to make a prototype for my car, but I honestly never felt sure, even if it sounded pretty interesting.

[RUM4MO]

I'm hoping at some point to get a decent lithium battery jump pack to keep in the car for emergencies.
You might want to look for something like that and just keep it in the boot/trunk.
Good lithium packs can hold their charge for quite a long time due to low internal resistance and therefore very low self-discharge.

I don't know if this is a "general thing" with these small lithium battery jump packs, but I'm sure that I've read many tales about people being very satisfied with them after using them to help people start their cars, then put them away only recharging them or topping them up "now and again", to then, after a couple of year even although keeping them charged up and using the built in self check to make that they were still good, to then attempt to use them to start a car with a slightly discharged battery - and they failed to do that. In one case, a guy was so impressed with the "quality" one that he bought, that his father also bought one, both looked after them well, but then this guy found his could not start a car, so he asked his father, who had the same unit, to use his as soon as he could/needed to, to check out its "health" - it now could not start car that had a partially discharged battery that should have been within the capabilities of that compact lithium battery jump pack - that shocked me enough to put aside any thoughts of spending money on one of these, which was annoying.

I'd hope that this sort of thing is something of the past - only one way to find out I'd guess!

I'd think that "low internal resistance" will only allow for high discharge/use current and not long term storage at full charge, by the way. There will be other mechanisms that allow/cause self-discharge like common electrolyte volume, for instance normal AGM batteries have cells that are packaged individually and so each gel pack is separate to the next one, and so self-discharge is extremely low, older basic flooded lead acid batteries have a common volume of acid and can or do end up with a trail of conducting salts at the bottom of the battery - so that acts like a permanent connected load and so discharges the battery over time.

[RUM4MO]

A friend of mine who studied electronical engineering told me about super capacitors to use in pair with a very small capacity lithium battery just for all the auxiliary services.
He says super capacitors have a huge crank power. He offered to make a prototype for my car, but I honestly never felt sure, even if it sounded pretty interesting.

I'm sure that some of the compact battery jump packs on sale will just be super capacitors - though maybe it is them that have a short(ish) life and so kill the capacity of these compact battery jump packs over time.