The push mower I use most of the time these days turned 50 this year-it's older than me. It's hard for me to imagine a scenario where I can't keep it going indefinitely short of throwing a rod through the block or something like that. I did change a few wear parts when I put it back into service last year after the(original) owner had let it sit idle for a few years-I needed an ignition coil(the big issue with it, and why he'd quit using it-it was deceptive as it ran but not correctly), a starter recoil spring, and an additional spring in the starter. I bushed the wheels with Oilite bushings to bring them back to round and fitted new wheel bolts, so it rolls easily and without any wobble. Even if this one does die, well there's more than a few similar ones to it in my garage, and there are plenty of others out there.
BTW, battery longevity-a lot comes down to both initial quality of the battery and using it within its design parameters. A lead acid battery that lives in a controlled environment and is kept at or near full charge can easily last years. Lithium Ion likes to live in the 20-80% charge range, but again will last years in a good quality battery that spends most of its time in an ideal environment. I bought my first MacBook Pro in 2012, and it was used regularly to 2015 and intermittently since then-it's still at around 82% of design life. I have had much older laptop batteries that work just fine. I set up a 2003 PowerBook for my dad for a specific program this past weekend. It was a 17" on an Apple factory battery, and those haven't even been avaialble in like 15 years. I pulled it out of the closet and told him that I made no promises of how good the battery would be, but darn if the thing didn't charge all the way up(it took its time) and when I tested it lasted an hour before I gave up. NiMH is probably the fussiest battery technology(IME) but treated right can still live a long healthy life.
The really amazing one to me is good quality NiCd. There's one particular model, or rather series of models, of camera flash I really like that were produced in various forms from the 1970s into the 2010s-if anyone is interested it's the Metz 45 series flashes. From the beginning they were sold with either a "basket" for 6 alkaline AAs, or with a 6 AA cell NiCd pack. I have about a dozen NiCd packs, most from the late 90s to mid 2000s. The vast majority still meet or exceed the advertised spec for flash recycle time(7 seconds claimed, most will do it in 6 seconds when charged) and when I've tested can, for the worst one, get about 40 full power flashes before recycle goes above 7 seconds. My best one can do around 55. For reference, the manuals say that a freshly charged NiCd pack is good for 50 full power flashes. I've only ever bothered to re-cell one pack, and it had a ~15 second recycle time on a full charge so I never bothered testing it further. Incidentally, I cleaned up a decent bit of corrosion from cell leakage when I rebuilt it, but it still worked. I have some 80s packs that will charge and hold a charge, one of which is close to in spec, the other of which will power and work the flash but comes in at around a 20 second recycle time. Metz came out with an updated NiMH pack to fit these flashes in the mid-2000s(they actually did it right-all of their NiMH packs regardless of the application use a thermal diode to determine full charge) and the couple I have are hit or miss as to how well they work. Granted it's worth mentioning in all of this that Metz is(or was) a German company and I know they used premium quality cells in everything(and charged a premium price for it...)-it's pretty rare that I find any of their nickel based batteries that are completely dead no matter how old. I'll also mention too that it's a shame NiCd has such poor energy density because in most other ways, IMO, it's a superior technology to NiMH. In 2023, though, an 1000mAh NiCd cell(which is about the limit for AA sized NiCd) is a hard sell when NiMH starts at around 1600mAh and you can find them on up to 2800mAh or so.