How many years do modern laptop batteries last?

It depends on a number of things. Heat kills lithium batteries fairly quickly. A battery will last much longer in a laptop with good cooling. Storing the battery at full charge is not good for it. Some laptops let you specify a maximum charge percentage. Only charging to 80% will make it last much longer. Charging to 40-50% if you know it's going to be plugged in for an extended period of time a good idea too. Fully discharging the battery is a lot worse for it that only discharging to 20%.

If you are not fully cycling the battery daily, you should be able to get 4-5 years if you treat it well.

The Framework laptops are some of the easiest laptops to replace the internal battery on and you can buy replacements directly from them.

Most internal batteries can be replaced provided that you can actually buy a replacement. Some laptops have glue or double sided tape holding the battery in place and prying a lithium pouch cell out is not the safest thing to do.

Mine is from 2017 and is still fine, not perfect but fine. has 700+ cycles and moderate to high usage. Most battery's can be replace quite simple pop the back cover of and disconnect it, except for tablets and some 2 in 1s they are glued together. Or you have to remove the Screen to get into it. good luck keeping the screen in 1 piece there.

For most laptop's batteries can last up to 5 years, if lucky up to 8 years like on of my older laptops.

In older laptop models batteries are very easy to remove and replace, in most cases you just take out the battery from the back.

With never laptops in most cases you need to remove the whole bottom cover and then you get access to the battery that is still pretty easy to remove. You just pull one wire and unscrew a couple of screws and you can just swap the battery.

Doesn't it depend on manufacturer?