Review (5/5): Make sure it is made in Holland
I've had my Norelco 6843XL for 11 years. I replaced the battery after nine years when it would hold a charge for only three or four shaves. The new battery is not quite as strong as the original but still will last for 10-12 shaves. I replaced the cutting heads when I got the new battery even though they still seemed to cut fine. I also changed them recently due to damaging a guard screen-my fault. One thing to check for is the country of manufacture: when the cutting head is removed my razor says Made in Holland in very small print around one of the drive shafts. I've heard that the razors made in China don't necessarily last as long. It cuts well everyday and otherwise has never required service.
2020 update: I've had the same Norelco 6843XL for 16.5 years now. I've replaced the battery twice; the most recent one is a larger capacity. It will last for about five weeks of daily shaving. The razor still performs as though it was new. I haven't replaced any other parts.