12.5 is just under 100% charged for a battery that has been sitting 8 hr without being charged / discharged. ( 12.66 is theoretical full charge but that can vary. )

What sort of voltage do you get while cranking
?

I've had batteries with good open circuit voltage but it dips too low under a load. How far the voltage drops depends on the load applied

You need to see what the trouble code is before going farther.

Also, a weak battery / bad connection isn't the best thing for a smart key, if the voltage droops too far during the key read write sequence, the system can brick. And of course , many blame the act of jump starting even though the damage was there before jump starting.