Hi,

 

writing this out since nobody replied to my previous posts with any information that would help me and will also possibly clarify some things to others.

 

I went to get my car battery replaced by a mechanic that was recommended to me, supposedly he had equipment necessary to code a new battery for a Škoda Octavia Mk IV. When I met him I told him my concerns and he guaranteed me that he is able to do it.

He simply disconnected the old battery and reconnected the new one, without any power supply keeping the car modules powered. He also needed to take out part of the air filter intake assembly for putting in a new battery, then he "coded" the new battery on some red tablet with a proper looking OBD cable. The tablet put out some beeps that would indicate that the coding was not a success but I didn't say anything since I didn't want to be a smart ass. When the car was turned on there were of course 20 warnings but after driving for like 50 meters they all disappeared.

 

When I came home I connected my VCDS only to find out that nothing was coded. I did not want to go back to that mechanic since he obviously didn't know what he is doing. I tried buying a SFD token service (one more shady looking than VAG logins) but it did not work, got scamed for 10€ but whatever.

 

My friend came over later today and he has a CARISTA evo module with a subscription. At first we couldn't change the battery coding, but when he read and deleted all the diagnostic error codes, he was able to change it, and I was able to verify it with my VCDS clone from aliexpress. I am pretty sure a OBD11 would also work for this - random tip, on the OBD11 website, register, put OBD11 with the VAG subscription in the cart, and don't buy it. Wait for an email from them and they will give you a 10% discount.

 

I am now very happy and satisfied. It is very noticable that the engine starts up quicker (like 1/2 second sooner), and with the VCDS I also looked at the analysis of starting behavior, and the starter draws a much higher current, while also creating a smaller voltage drop on the battery. The internal resistance as shown by VCDS is also much lower. Will keep you updated how long the AGM battery will last me.

 

Cost-wise, the 72 Ah AGM battery was 160€ while I could get an EFB battery of similar capacity for 100€. Dealer's garage would charge me around 300€ without them being able to tell me if they will put a cheapo EFB or an AGM battery.

 

I can also add something to this but I can't say for 100%.

I built a testing rig to measure charge and discharge of the used 12V EFB+ battery, supposedly 72Ah when new.

 

I am a bit surprised and for this reason doubtful but seems like the battery only has about 25 Ah capacity left, so about 35%, while the on board system was showing as it having 83% of capacity left - usable battery capacity when full.

 

Sadly I do not have a brand new battery to test this out and see how much charge I can put in and take out, so take this with a big amount of salt, but basically I did this 2 or 3 times now, measuring how much energy in Wh and Ah I put in and get out and it seems to be at the 20 - 25Ah range.

 

In the screenshot you can see all the curves, altough because of some error the top left is marked "Wh", it actually represents the voltage, I current in amps, and below power and amper hours, This is the discharege of a fully charged battery.

And here are the charging charts of a fully discharged battery (around 11.6V empty)



For anyone wondering - this was done with INA211current sensor and ESP32 microcontroler, the dummy load was a heater element.

 

I also did another test where I connected the used battery to a 12V to 230V inverter, connected a handheld vaccum machine to it, and it was able to put out about 500W, powering the vaccum, while the voltage on the battery dropped to 10.8V, so about 2V, if I can trust the voltage indicator on the inverter. Using a much smaller 12V battery, that with my tests puts out about 12Ah of capacity, the vacuum would not even start because the voltage drop on a much smaller (not a car lead acid battery) battery is so high, the inverter doesn't work.

I am planing to use this used battery with an inverter for camping reasons or for a portable 12V refrigerator I have, should be able to power it for like 2-3 hours.

Beat in mind that a lead acid battery can only deliver 50% of the stated capacity and, depending on the battery, can only deliver that a specified number of times.  For your camping fridge you should get 3hours at 12V continuous running.  This may extend to 6 hours if the external temperature is not to hot.  The fridge in my camper van runs at 5A with a duty cycle of around 50%.  This gives me 7 hours off a 75AH battery which is rated to 200 deep discharges.

Another update

Surprisingly, the car computer estimated charge and performance degradation has already increased ... Like wtf after only 100 Ah of total re-charge. Also, the adapted capacity shows up as 84 Ah although its was and still is coded as 72 Ah. This number automatically went up from last time (see first post).
The internal resistance also shows up as a bit increased

 

 

 

I will be posting further updates about the battery here: