Dyson DC44, their second cordless (first one DC38, the later DC58 was re-branded to V8 or V6), bought in 2016. Apart from power adaptor failure, it is still working very well. Battery may have degraded slightly over the years, but still works well enough to function as our only vacuum.
It probably helps I use it to clean kitchen after dinner and don't plug it in until next morning. So instead of keeping it charged at 100% all the time, I let it sit at lower state of charge for many hours a day. Li-on battery are best stored at around 50% charged.
I'd buy another Li-on powered cordless without hesitation. They are so easy to use and can last a long time.
My cordless drill however, not Li-on battery, its battery sucks.......