glad it was covered under the warranty. I see so many on these boards that are not and it's almost always something simple like a lifter. $10k later you get a reman engine and a truck worth 12k. that's the non hybrids, these engines are even more of a hassle because of the low numbers out there.
if you're into it, I really like having torque app on my phone to watch the hybrid data from time to time. it's just handy and only 5$ for the app, some manually entered PIDs and a 20$ dongle. you do need to be a non apple device for torque app. if you only have apple, there's others you can try and might have the data, but you can't add anything if they don't and of course nothing is cheap with them haha.
the real thing you need to do much with these is a tech 2. a 300$ clone one will do, it will allow you to access all the codes in all modules(if I remember right my yukon has 32 modules it can communicate with) you won't see but 1 from a normal obd2 scanner, and run a bunch of tests. it's very helpful to see what is throwing that service hybrid system light.
there's a code behind it. once you find it, you can get monthly or yearly access to the repair guides that shops use which will have trouble trees to walk you thru testing based on the codes. I have access to some stuff I can look up codes on too and post up. but if it's not simple, it is nicer to have you own access.
the more you read about these trucks on different message boards, the more you'll see thread after thread that dealerships can't or won't do even basic troubleshooting on these trucks. they are untrained on this older tech and the flat rate pay system rewards parts swapping not trouble shooting. Sadly keeping these trucks running long term turns the owners into mechanics lol or at home diagnostic techs.
with the miles you got out of your referb battery, it might be more cost effective to get another one, or just drive your truck in M4 mode which keeps it from going into auto stop to. avoid the bucking. but the lithium drop ins are from a small company called projectlithium. I don't know if I can't link directly, since not a site sponsor and all that. but that will get you there. it's mostly prius stuff, but since the prius stuff is the same, they have a set for our trucks. of course more expensive because we have almost twice the cells. your 40 nmhi cells are replaced by 20 lifepo4 cells. again thou, I'm having good luck with them. but the internet argument is you're using a nmhi controller to charge and discharge lithium batteries. it's a long story why it works, and even then some thing they won't last long term but it's not the normal lithium you hear catching fire and stuff. it's the lifepo4 chemistry that is very stable, and at worst you'd have to throw them directly in a fire for them to burn up. it's not the same stuff you cyber truck will have.
I'd be super interested in how your cyber truck ownership goes too. Hopefully you stick around.