M's have 2 year/2000 hour warranty whichever comes first (usually 2 yr). OR, another year on powertrain, as I remember. Powertrain consists of internally lubricated parts and the warranty handbook outlines it pretty good. 5 years on emissions.
Your tractor was a 2017? It's 2021. If you purchased in 2017, your warranty is expired. Emissions might still have some warranty but here is the deal....read on.
Limited warranty is administered by dealer. It covers defects in manufacturing and workmanship for a certain period of time. That is one of the limitations (hence "limited warranty"). It is not lifetime warranty to my knowledge. With that said, emissions "might" help with the ecu. The problem with that is, kubota's warranty dept needs to know what the ROOT cause of the failure is. If they were able to deem that the root cause was a failed battery, a battery is coverd by the original warranty only (and actually may have it's own separate warranty?). Since the root cause has nothing to do with what powertrain and emissions limited warranty covers, you have a problem to deal with.
Notice I am not defending Kubota or anyone else here, it's just the way warranty works. Warranty is almost always called a "limited warranty" because, as said, has limitations. It is not insurance although if you had insurance they "might" take care of you (although they generally don't cover mechanical failures that are not accidental).
And finally all companies including Kubota are cracking down on warranty abuse. They are going by the books and anything "gray" is not covered. Unfortunate but it's only a sign of the times. People (and dealers) have been abusing warranty forever; and when I worked at the dealer I saw it OFTEN (daily several times a day usually), particular with lawn & garden equipment (Kommanders come to mind....). Just within the last year I saw changes in the warranty department that were not condusive to good customer service. I didn't and do not expect them to pay for everything, but there were times that they should have, but didn't--hence the phrase "gray area"--they were generally repairs that were not black and white defective. With that in mind, 88% of all of my warranty claims from 2019 through 2020 were not really warranty, they were obvious neglect, abuse, and accident, although we felt sorry for the consumer and took care of them. Kubota is smart and they know. Nowadays they want ECU data (codes), pictures, they're doing fluid analyses, they need to know this stuff to know if a failure it their fault or the fault of someone else, and the biggest reason for that is NOT so much to get out of paying for something, rather to point them in a direction that helps them build better equipment. Remember they have to compete with Deere, and now Cat, Komatsu, New Holland, and a bunch of others, so their product and service needs to be competitive. Unfortunately it also means that some repairs just aren't free anymore.
If your dealer doesn't want to give you any clear cut guidance or good explanation, move up the ladder-call customer service, and they'll get the field service rep involved.