Battery upgrade: from Lead/Acid to AGM

[2226]

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.

I'm sure some are, but I've seen proper lithium ion packs that still have full charge after 6 months of storage.
Heck, if I my 18650 and 21700 cells here drop maybe 1% after sitting for several months.

I have to find that youtube video where the guy replaced his car battery with super capacitors. In all honest, I wouldn't want to work around that.

[2226]

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.

My understanding is then pretty much out of sync.
Yes, low internal resistance will give bigger discharge.
I've always understood that it and chemical makeup of the battery affect self discharge.

Homework time.

[Jay-Jay]

I remember my friend did some calcs and extimated that supercapacitors would loose all their energy after 31 days straight of not using the car.
Maybe real life conditions might reduce that extimation, but if you use the car almost everyday, it should make the problem completely disappear. In theory.
But I never felt confident to give them a try, even if it all sounded promising, like all the YouTube videos of people who are using supercapacitors since years in their cars.

[2226]

I remember my friend did some calcs and extimated that supercapacitors would loose all their energy after 31 days straight of not using the car.
Maybe real life conditions might reduce that extimation, but if you use the car almost everyday, it should make the problem completely disappear. In theory.
But I never felt confident to give them a try, even if it all sounded promising, like all the YouTube videos of people who are using supercapacitors since years in their cars.

They also lose their charge super instantly if you mistakenly short a wrench across their terminals. Right through you.

[RUM4MO]

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.

My understanding is then pretty much out of sync.
Yes, low internal resistance will give bigger discharge.
I've always understood that it and chemical makeup of the battery affect self discharge.

Homework time.

Maybe I didn't quite write that to read as I intended, the internal resistance of a battery will always, ignoring other health issues it has, be the limiting factor on its ability to deliver high current, as the internal resistance increases probably with age/wear, if all other factors remain as they were for that battery when new, then its ability to deliver high current will decrease.

I seem to remember, from my days of using electro dynamic shakers, that for maximum power delivery, the power supply output impedance should be near enough the same as its load input impedance, car a car "starter battery" the main load will be the starter motor.

[Jay-Jay]

Well, the Yuasa AGM battery has been delivered to me this morning.
I immediately connected my battery charger to it. It was at almost half charged.
Now, after almost 9 hours, it is almost full.

As you can see, at the last phase of charging, the voltage is floating at about 14,5-14,7V (which is never erogated by my alternator, as I already wrote in previous posts).
The instructions manual of my battery charger says that program 2 (the one I selected) is specific for classic acid/lead batteries under cold conditions or for AGM batteries:

As soon as the screen will show "FUL", I will install it on the car.
Finger crossed nothing is going to explode

[Johntheo1]

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.

My understanding is then pretty much out of sync.
Yes, low internal resistance will give bigger discharge.
I've always understood that it and chemical makeup of the battery affect self discharge.

Homework time.

Maybe I didn't quite write that to read as I intended, the internal resistance of a battery will always, ignoring other health issues it has, be the limiting factor on its ability to deliver high current, as the internal resistance increases probably with age/wear, if all other factors remain as they were for that battery when new, then its ability to deliver high current will decrease.

I seem to remember, from my days of using electro dynamic shakers, that for maximum power delivery, the power supply output impedance should be near enough the same as its load input impedance, car a car "starter battery" the main load will be the starter motor.

VCDS gives two internal resistances for my 5.5 year old petrol Polo with a 59AH EFB battery, one gives a 7.6mohms, the other "not normed" 5.2mohms.
With a M.meter on the battery terminals, the volt drop was 1.82V, from 12.27V to 10.45V, this gives a starter draw of 239A, so probably a reasonable indication of the battery internal resistance?, VCDS shows a remaining battery capacity of 31AH.

[Jay-Jay]

Well, the battery got fully charged.


This morning I installed it.
Here's a few photos



First impressions: charge voltage seems to be slightly higher and more stable than before.
In other words, even when engine warms up, it doesn't get as low as with old battery, but it stays always at about 14V.
I honestly can't understand why, since my alternator shouldn't be so smart to understand what battery type is installed.
Maybe it's simply because my alternator works better with smaller capacity batteries (maybe 74ah was a bit too much). Who knows.
But I feel happy about it and I hope it will last longer than classic acid/lead batteries.

[2226]

Voltage will go up as the battery charges, so yes probably seems lower on the 74Ah as it was charged up less (more capacity to fill).

[Johntheo1]

Don't know what year car you have but its quite possible that it has this smart Alternator system where basically the battery is only charged at 14.3/14.8V when the car is on overrun, it charges at ~ 13.2/13.6V for the remaining time. If you have this system then the BMS should be told what type battery is installed, mine is a EFB (from new), buy a DVM (digital volt meter), plug it into the power point near the gear lever, you can then glance at it occasionally while driving and see exactly what is happening. All my older VWs (non smart charging) charged at a constant 14.2/14.5V and the batteries literally lasted almost forever, and only changed as a precautionery measure after 10/12 years.

[Jay-Jay]

My Polo is from 2010 and it doesn't have start&stop function, so it doesn't have a smart alternator nor a control unit dedicated to battery charging.
My alternator works with ambient temperature (more precisely, engine bay temperatures). As soon as temp raises, it lowers the charging voltage.
It doesn't have any sensor nor "sense wire" to understand what battery type is installed.
It never charged more than 14.4V, but for a very short time. Usually it charges at slightly under 14V.
Surprisingly with the AGM battery it charges at a slightly higher voltage and when it drops the charging voltage due to engine bay temp, it doesn't get as low as with classic lead/acid batteries.
Another good thing I noticed is this.
With classic acid/lead batteries, even new ones, everytime I was getting into my car, battery voltage was never higher than 12,3V.
With this AGM battery I always measure a strong value of 12,7-12,8V. So it seems like it better keeps its charge during the night.

[Johntheo1]

My Polo is from 2010 and it doesn't have start&stop function, so it doesn't have a smart alternator nor a control unit dedicated to battery charging.
My alternator works with ambient temperature (more precisely, engine bay temperatures). As soon as temp raises, it lowers the charging voltage.
It doesn't have any sensor nor "sense wire" to understand what battery type is installed.
It never charged more than 14.4V, but for a very short time. Usually it charges at slightly under 14V.
Surprisingly with the AGM battery it charges at a slightly higher voltage and when it drops the charging voltage due to engine bay temp, it doesn't get as low as with classic lead/acid batteries.
Another good thing I noticed is this.
With classic acid/lead batteries, even new ones, everytime I was getting into my car, battery voltage was never higher than 12,3V.
With this AGM battery I always measure a strong value of 12,7-12,8V. So it seems like it better keeps its charge during the night.

My battery voltage (per VCDS) was 12.35V and (derived) 12.6V battery voltage at rest and a SOC of 85% so your voltage, above at 12.3V would probably give a fairly similar SOC, a battery lead should be disconnected for around a hour or so if the battery at rest voltage is measured with a M.meter at the battery terminals, the VCDS (at rest) figure to give a 85% SOC seems to ~ match a old chart, below. (VCDS also gives a "usable battery charge" of 31AH (59AH EFB battery, 5.5years old).

Volts Capacity % volts/cell
11.51 10 1.918
11.66 20 1.943
11.81 30 1.968
11.96 40 1.993
12.10 50 2.017
12.24 60 2.040
12.37 70 2.062
12.50 80 2.083
12.62 90 2.103
12.73 100 2.122