But surely you (or your workplace) have a backup plan if your laptop needs service that takes a few days. What would you do if you need a new screen, or a new hard drive, or a new fan... It's not like a laptop repair that takes a few days should be a big shock to anyone who's owned a few laptops (Apple or otherwise).
By the way, one of the things that the $500 Joint Venture program gets you at Apple is a loaner computer while your machine is out for service. So that's one option.
The other option, which we use at my work, is we have a spare laptop. It gets used for a number of purposes, one of which is a loaner for repairs.
But if 1 piece of machinery really is that critical to your business, you'll have an identical standby ready to go when your primary one eventually craps out.
I've decided to let Apple handle inventorying my standby machine. I can walk into an Apple store and 5 minutes later be ready to go again. Then the high resale value of my old machine makes it easy to sell on craigslist.
I've never seen the battery compartment be the source of physical issues. Typically it is the hinges on the LCD that give up or the case cracks in one of the four corners.
Mostly the case remains solid and the hardware within blows up.
If you keep your laptops long enough, you'll eventually have to deal with replacing a battery. My two-year old Dell latitude E6530 is solid (and admittedly heavy), with no noticeable flex. It has an easily replaceable battery as well as user-upgradeable RAM! I'd call it a well-made piece of hardware. I expect to replace the battery in the next year or so (the battery is starting to show its age by now, but at least it still works).
A bit off-topic: My previous laptop, a C2D Macbook Pro (old enough it had a replaceable battery) developed a swollen battery after 2 years. At the 3 year mark I had to open it up and replace a failed case fan (and a hard drive). Also, the optical drive failed within the first year, as did its warranty replacement. I eventually gave up on that (and removed the drive so it would stop churning incessantly) and bought an external USB drive.
My laptops last 4-5 years. This battery failure was at 1.5 years. I just replaced mine after 2 years.