12v battery replacement

I see the same thing. A short, sharp dip before the 20 minute charge starts, exactly like your graph shows. This does not always happen, just as it does not always happen for you. In addition, I always see a lesser dip, after the charge cycle completes. My voltage drops to 12.71 and it takes about 20 minutes (after the charge cycle completed) for it to come back up to 12.85.
So that is that.

I think I understand how my battery got "fixed". Stratification, where the acid/electrolyte becomes more concentrated at the bottom, happens
when the battery sits for a long time unused. This happened, while my car was at the dealer, waiting 8 months for the HV battery.
The recommended remedy is an "equalizing charge" ie. charging the battery for an hour or 2 at 16V. This is apparently an arrow in the quiver, for a marginal flooded battery, it is worth a shot.
At 16V, electrolysis results in vigorous bubble forming, which mixes up the electrolite. The caveat is to do this in a well-ventillated place, and
for flooded batteries only.

I have unwittingly done this. My shop charger has different AMP settings, at 40 AMPs it charges at around 16V. I charged the Rocket off the vehicle 2x 1 hours. So that is one mystery figured out.

Note, that for AGM batteries this is neither necessary, nor recommended. AGM-s do not suffer from stratification, and excessive gas formation is actually bad for them.

 

Kiwi, how do you capture your battery graphs from BM2?

 

I just do a screenshot and copy.

 

Your smartphone will have a means to capture the screen and save as a photo which you can copy and paste to the forum, just google that question for your particular model.

 

I went ahead and swapped the OEM Rocket battery for an AC Delco AGM. I did the
reset procedure recommended by Kiwi. Initially the BMS varies the charging voltage, it settled down now to 14.67V. It now charges this battery to a bit over 13V, if left sitting, on the usual 4 hour schedule.

 

Great info! How did you get the graph above?

 

The battery graphs shown in this thread are produced by BM2, a combination of a mobile app and a simple piece of hardware attached to the battery. Search for BM2 on amazon. The graphs are then screen-captured on the mobile device.

 

quoting from a while back:

So I've now been bit by the 12 volt battery failure. Fortunately I'd planned for this and had the jumpstart pack accessible and all set to go, simply plugged it in since I'd installed the mating NOCO plug on the battery. Started the car, fired up the BMS app and took a look around. I confirmed that the rear door was securely closed, the car had been sitting locked up in the garage for three days.

The reason I quoted the part about cell balancing, is that this failure occurred after I did something unusual: charged the traction battery to 100% twice, and both times postponed the trip that I had been planning where I'd need that extra range.

It's very noticable, that since the middle of last week battery drain between 12 volt battery charging periods was much higher than normal, finally causing the battery to be drained to 9 volts two days ago.

I left the car in utility mode for half an hour, and after that the battery was charged to the point where its voltage stayed above twelve volts. After shutting the car off for a while, the orange light on the hood lit up and the car began charging the battery while being turned off.

The charging has since stopped with the battery voltage back up to 12.9 volts.

The question is, does charging to 100% sometimes kick the BMS into some state where it's desperately trying to rebalance the battery and thus quickly draining the 12 volt battery? At the moment all the cells are reading 4.14 volts.

I'm about to take it out for a drive and knock the SOC down below nearly 100% in hopes that this will prevent the battery from being discharged like this again.

Here are the traction battery charge and discharge events that can be matched up with the BMS graphs:

May 7, 07:00: finished charging to 100%
May 10-11: 200+ mile trip beginning at around 21:00 and ending around 05:00
May 12: 6 mile trip starting at 5 pm
May 12: 22:30: start charging to 100%
May 13, 01:30: finish charging to 100%
May 13, 12:00: battery falls to 9 volts
May 16, 17:29: jumpstarted

 

I don’t think this has anything to do with charging to 100% or balancing.

Either your 12V battery has failed or there is a significant drain happening while parked.

I’d suggest either replacing the battery as a test or booking into the dealer either now or if that test indicates the problem is elsewhere.

 

@mtd, I don’t see anything in your graphs to identify a current cause of failure, rather I see a battery that was already in terminal decline prior to this event. In good condition, a 12v will quickly recover from a current drain to a stable level - your graphs show consistent declines in voltage between top-ups.
Below is a graph of my 5 yr old Kona 12v over 15 days - it has not had any significant discharge events. Voltage between 24 hr charging top-ups is steady at 12.63v as shown.

 

I should have mentioned, this is a 2023 Kona that is only a year and four months old, so I doubt that the battery has signficantly failed this quickly.

The one possible load is an OBDII dongle that I've left plugged in without any noticeable battery drain for a few months now, though this is likely one of the few times I've let the car sit for a few days without having an opportunity to charge while driving. I'll now leave it unplugged and see if that corrects the problem.

 

As a note, the three smaller 'steps' seen in 2 of your graphs are (IMO) the car 'reacquainting itself' with your 12V battery. In normal conditions that only happens when the 12V battery is disconnected, but in this case perhaps it's due to voltage drop below the minimum operating level. I suspect the car is establishing either or both the internal resistance or discharge resilience of the battery.

Just to the left and higher, the trimmed-off rising edge is certainly the LDC current-limiting due to encountering a severely-discharged battery. It's probably seeing in the order of perhaps over 100A for numerous minutes. I saw this once on my own car just after the dealer completed a BMS update.



Another possible but probably unlikely cause could be leaving an un-powered EVSE plugged into the car.


Or this:


This is typical what I see day after day. Here, after 2 short drives at 1715 and 1815 the BMS is doing a cell balance. This Kona, by the way, does not have telematics enabled in the media centre unit and there's no service here, so no related drain.

 

Mtd,

What type of 12v battery do you have in the car? Is it a plain lead-acid battery? Then it is not impossible it has stratified, or failed already.
The lead acid batteries the dealers now install only have a 1 year warranty, and could have issues like electrolite stratification,
or water evaporation. Flooded batteries do not like deep discharges, and a surprisingly small number of these tend to
really hurt them.

OTOH the car may have been shipped with some type of maintenance free battery that may have a longer warranty.
I think the original Rocket MF battery had a 2 year.

Your graphs show massive voltage drops. This is either due to significant drain, or maybe small current drain,
but a 12v battery that is unable to maintain voltage in face of that drain.
It looks more like drain to me, because the drainage pattern I have seen on my car or on other people's graphs tends to be more random,
and the voltage seems to be bouncing back without any charge events. This looks like a healthy battery does this type of bounce
via chemical reaction. When the battery is being charged, you just see a flat line at the charging voltage.

Another oddity, I see charge windows where your car charges the 12v battery at only 13V instead of the typical 14.6x.
Kiwi, do you have a theory why might that happen? Does the 12v charging system "measure and analyze" the 12v battery?

I had a problem once, with and OBDII dongle killing the battery on a different car before (a Mercedes cla) so removing that
may be a good idea.

If you have a shop charger, you could charge the 12v battery (off the car) at 40 amp setting, 2x 1 hour, to recondition it.
If it is a lead acid, having inspection/water refill plugs on top, inspect, and if you can see the top of the plates, top off with distilled water.
Remove the OBDII dongle, and if the problem persists have the dealer run diagnostics.