Reason I'm asking is, I am contemplating doing a battery change. Macbook still works really fine on Mojave, but battery is almost hitting 80% capacity, albeit at 300+ cycles..
I've just bought a refurbished one. I'm hoping they'll be supported for a few more years yet. It can natively run Mojave and Catalina due to its Metal-compatible graphics.
Apple's typical support range for repairs is 5 years after they stop making them. Their security updates often follow similar numbers.
These models were replaced in 2014, so they could be axed in any future cycle. You can see for yourself. Some of the 2013 13" models are marked vintage for repair purposes. I wouldn't anticipate many years of support going forward.