A mechanical watch never needs a battery. It runs on the movement of your wrist (automatic) or by winding (manual). It can be serviced by any competent watchmaker anywhere in the world for €60 to €150 every 5 to 10 years. The movement inside a well-maintained mechanical watch lasts generations. Under €500, three brands stand out for the quality of their movements and their repairability.
Also read: Best BIFL Leather Wallet: What to Look For and Which Ones Last and Best BIFL Multitool: Leatherman Wave+ vs Victorinox Swiss Army
Seiko
Seiko has made its own movements in Japan since 1881. The Seiko 5 Sports series (€150 to €300) uses the 4R35 and 4R36 movements: accurate to -35/+45 seconds per day, which is not chronometer-grade but acceptable for everyday use. The parts are available worldwide and any watchmaker can service them. The Seiko Presage series (€300 to €500) uses better-regulated movements (3R65, 4R57) with higher finishing quality. For a first mechanical watch that will last a lifetime: the Seiko 5 Sports.
Tissot
Tissot is a Swiss brand owned by Swatch Group and uses ETA movements, the most widely serviced Swiss movements in the world. The PR 100 Automatic (€350) and Le Locle Automatic (€450) are the most recommended BIFL models. Tissot offers a 2-year warranty and ETA movements are serviceable by virtually every Swiss-trained watchmaker. The trade-off: Swatch Group has been restricting ETA movement sales to third parties, which may eventually affect parts availability.
Orient
Orient is a Japanese brand owned by Epson/Seiko that makes its own movements and is known for offering the best value mechanical watches in the world. The Bambino series (€150 to €200) is a dress watch with Orient's in-house F6724 movement, accurate to -10/+30 seconds per day. The Mako and Ray dive watch series (€150 to €200) are the most recommended budget dive watches. Orient movements are serviceable and parts are available.
The Recommendation
For a first mechanical watch with the best worldwide service network: Seiko 5 Sports. For a step up in finishing and Swiss movement serviceability: Tissot Le Locle. For the best value mechanical watch available: Orient Bambino or Mako. All three can be serviced and worn for 50 years.