Thanks for posting all that. Given that the battery has built in electronics, with somewhat unknown (to us) behavior, I think its going to be difficult for us to guess what is "optimal" charging. That is, there is some interaction that takes place between the external charger modes and how the battery electronics interpret and respond to those modes. I think that generalizations we see about the different charging profiles for FLA, and the different variants of the Lithium Ion batteries may not apply when there is essentially a non-liner function that sits between the battery and the charger. In other words, I think one can use the GM CTEK charger without concern, and according to CTEK some of their other models will work as well, because they are recommended, and probably tested with the Eray battery. But I'm not so sure about trying to use other chargers. My thought is that they need to be compatible not just with the type of Lithium Ion battery, but also compatible with the built battery management system that interacts with the charging system (both an external charger and the car charging system).

I see you mentioned a Tech Link article but I did not see where you provided the link to it - sorry if I missed it - but here is that link:

https://gm-techlink.com/wp-content/u...April_2024.pdf

I did not know that CTEK chargers would estimate internal resistance and behave accordingly. But in another thread, recently, discussing battery and charging system related stuff, I showed some math (simple V=IR based), that showed if the charger takes a voltage measurement and current measurement (by applying two different charging voltages), that is enough information to estimate both the internal voltage of the battery and the internal resistance of the battery. Sounds like that is what the CTEK charger does. The C8 charging system takes such measurements as well, and could also do that, but I do not know if it does so. I have also wondered if the something like that could be used to determine the battery type.

The 2020 version of the Service Manual, which pre-dates Eray, indicates that it (the car now, not the charger) has a sulfation mode:
"Battery Sulfation Mode - The BCM will enter this mode when the interpreted Generator output voltage is less than 13.2 V for 45 minutes. When this condition exists the
BCM will enter Charge Mode for 2-3 minutes. The BCM will then determine which mode to enter depending on voltage requirements."

Of course, it could have been, and probably was, updated since 2020 for the Eray - and it could be an incomplete explanation as well. It does not say anything about estimating internal resistance. I see that the tech-link article mentions a couple of things I found interesting. First, it says "The lithium-ion battery will not decay like a lead-acid battery. The battery health will fall off sharply; it will never provide a slow crank." In other words its going be "no crank" instead of "slow crank". But......it also says "If the 12V lithium-ion battery requires replacement, the vehicle will set DTCs in accordance with emissions regulations. The DTCs should be recorded on the warranty claim". The Stingray has been known to tell owners that a battery is "low", but I'm not aware of any messages about replacing the battery. So, this suggests that there have been updates to the charging system. Obviously I suppose, since its also tied in with the high voltage system.

The tech link article also says "he 12V lithium-ion battery is charged by the K1 14V Power Module while the vehicle is operating in the EV modes (Stealth and Shuttle modes)," which I think you stated. I wonder if the high voltage battery pack does, or could also be used to maintain the 12V lithium-ion battery while the car is off, or in storage.

 

https://gm-techlink.com/wp-content/u...April_2024.pdf

 

Maybe your point is that the article appears to confirm that the battery does have a built-in BMS, as I speculated? If so, that's a good point!

Still, there's lots more detail I wish was included.

 

That's right. Not only does it have one, but "The battery communicates via CAN to the K9 Body Control Module (BCM) to provide status and DTCs. GDS2 can be used to read scan tool information directly from the 12V LiB under the K244 Battery Management Control Module."

Since it communicates directly with BCM via the CAN, it suggests that the battery contains electronics and connections unique to the C8, or GM cars. And it could be proprietary, if its using the network encryption. In the FLA versions, there is an external battery monitor module that resides at the negative battery terminal and is electrically between the battery negative terminal and the negative battery cable. Is that there with the Eray battery, or is it completely replaced the battery internal logic?

 

^^^^
Yep, from what the fellows with RV's have and have investigated all Li-Ion 12 volt batteries have basic BMS to protect the batteries from overcharging etc. One did say the cheap ones from China are not as good and don't supply the rear-outs etc as others. I agree with your thought the E-Ray appears to use a GM system that may also control the charge level they desire! From my driving measurements that appears to be ~13.3 volts.

It's fun since I use Stop/Start when I'm in MY Mode I can see the alternator voltage (shown on the Dash Display as Battery voltage.) But as soon as the engine shuts off when I stop for a Red light it quickly shows battery voltage, usually ~13.3 volts when I have driven long enough to have it "fully charged" for what GM wants it to be. As noted, if at a long light and the engine is stopped it may drop to 13.2. Once the engine starts, it goes to ~13.5 for a short time, then 13.4 and after a few miles back to 13.3. I assume, as with my 2020 C8 the battery is sufficiently charged (13.3 is ~ 85% capacity) then the alternator is just suppling the electrical needs for AC Fans, Sound System, whatever Lights etc BUT not enough to further charge the battery.

 

Looks like a basic connection to the negative terminal, but in this photo you can also see the two connections on the left side that I was talking about before.

 

With regards to the desulfation mode, not all desulfation modes would be bad for a LiFePO4 battery. Some desulfation modes use high frequency, high voltage which I'm assuming a LiFePO4 battery wouldn't like. My RV has a charger/maintainer designed for FLA batteries and has a desulfation mode that can't be disabled. However, the desulfation mode just periodically "overcharged" the FLA batteries to 14.4 volts which happens to be the voltage that LiFePO4 batteries need to have to be charged to 100%. The problem is keeping LiFePO4 batteries charged to 100% shortens their life so I unplug the charger when I'm not using the camper. It also has a boost mode that charges at 14.4 volts so I can use that to charge the LiFePO4 batteries to 100% when needed.

 

I should have said a little more about the C8 sulfation mode, as described in the 2020 Service Manual. It says the sulfation mode is simply invoking the charge mode for a period of 2-3 minutes. And the target charging voltage for the charge mode says "13.9-15.5 V, depending on the battery state of charge and estimated battery temperature". Its probably all changed for the Eray, but I think we can assume that charge mode (or whatever its now named) will interact correctly with the Lithium Ion battery and its internal electronics.

 

Yep that connector is probably what was referred to as the CAN signal connectors in the WRONG statement in the 2024 Owner's Manual. That was part of my concern when I got my E-Ray in February! Was in the PDF I downloaded (along with IF the EV battery is discharged it should be plugged into to a charger!) My written Owner's Manual had removed that foolish EV battery on charger statement but kept the if the car sits for a week..."

 

My guesses. The connector, circled in red, is connecting to the " K244 Battery Management Control Module". Circled in blue is where the Battery Monitor Module would reside in the Stingray with the FLA. And it appears to me missing on the Eray. So, it appears to have been "replaced" by what is inside of the battery. I do not know what the other connection is - do these require a vent?

This is starting to look like when the battery is replaced, its going to need to be a GM specific part number with the connections we see in the photo.

 

The tech-link article continues on page 5.....and says this as well: "Do not replace a 12V LiB with a lead-acid battery in a customer- pay scenario, as a number of vehicle conditions may occur with the missing control module."

 

I'll see if I can figure out where that hose goes, but I still wonder if it carries coolant for the battery and/or BMS.

 

There is probably info in an up to date Service Manual. The illustration in the tech-link article looks like the ones I find in my service manual, and may have come from a battery replacement procedure. Unfortunately the illustration does not show the connecting wires/tube. It gives a "slight" clue - you can see the opening appears hollow. I looked lithium ion battery vents and they do require venting. Of course so do FLA batteries and now-a-days we don't have vent tubes. My 1937 Ford actually did come from the factory with a 6 volt battery that had "nipples" on the three caps, and a tube connected to them and vented to an opening in the fender well. Its quite rare to find that original tube and caps - very very rare.

 

@Andybump Good call... the tube dead ends. It's a vent tube!

 

Wow… enough opinions to write a small book. I don’t own an ERay but I’m thinking that I would just start to car every month and let run for a half hour. Yes it’s not a good ideal not to run the car unless the oil can be brought to temperature for a certain amount of time. But just to keep the high voltage batteries charged until spring seems like something to consider.

 

One more piece of Li-Ion car battery Triva:
A lithium-ion car battery is balanced by using a Battery Management System (BMS) which monitors the voltage of each individual cell within the battery pack and actively diverts a small amount of current from cells with higher voltage to those with lower voltage, ensuring all cells are charged at a relatively equal level, maximizing battery life and performance; this process is often called "cell balancing."

 

Well not true. The ERay also uses a Lion battery to start the ice engine. When I last talked to Harlan he suggested not to use that Lion starting battery in any ice only Corvette because the charging electronics are different enough to cause issues in the ice cars. However there are non GM Lion batteries that claim to work just fine in the ice versions. This one is safe to use in a ice only corvette.

 

Probably because the E-Ray's Li-Ion 12V batteries BMS is apart of the E-Ray's components and not integrated into the battery. So if plugged into the Z06, there could be issues since it doesn't have the BMS to handle the electricity that is programmed for the lead acid.

Third-party Li-Ion 12V batteries have their own BMS integrated into the battery that is able to take the power from the car and safely handle it.

 

Yes exactly currently the GM Lion battery is an integral part of the electrical system and can only be swapped out for another GM Lion battery when replacing it.

 

Wow ! Very impressive, thanks JerryU !! Because of the Weather here in the Pacific Northwest, haven’t been able to drive much. Consequently have to keep a Charger on the eray. Originally purchased a Battery Tender brand 3 Amp AGM-Lithium charger. Unfortunately, would not work correctly or even register a charge. So, then purchased a CTK brand Lithium battery charger and it works perfectly.