Laptop Battery Life Recommendations
First of all, if your laptop is really used as a compact desktop at home or at work and in fact doesn't travel much, removing the battery robs you of the usb ports functions as a 'UPS'. Solution is to obtain a real Ups. For a laptop, you only desire a small one (300 to 350VA), these can be found for $40 or less (sometimes even 'free after rebate'), and an UPS is a lot cheaper than a new $200+ lithium battery as an UPS but destroying it over a time period 6 to year or so in the work.
And the next thing, notwithstanding common advice to remove a laptop battery that is not needed and not being used, the battery needs to be exercised 2 to 4 times each year. So, once in a while, put it within the laptop, draw it down to about 25% and then charge it back up to about 60% (or 100% and then back down to 60%; Lithium batteries store better with a less than full charge although within personal experience I've not found the impact on really matter very much).
And finally, it's probably not a choice to remove the car battery while you are staying in an accommodation for a few days, even if you won't need this particular. The risk of forgetting the battery in the hotel when you check out is significant and you can mitigate this as well as leaving the battery with your laptop bag, but ask anyone who uses PC Cards about 'lost dongle cables'.
Also note that lithium batteries possess a finite and limited life in the number of charge/discharge cycles. Although this varies by battery model, it's in the low-to-mid hundreds (say 300 to 600 cycles as a range). If you're using your battery while traveling, charging and discharging it on a daily basis, this fact will 'get you' no matter what you do. But, more commonly, people find out they have destroyed their battery without ever really using it, by leaving it in the laptop while the laptop was plugged in continuously. And we now already covered the response to that problem.
One last comment, given the associated with laptop batteries, it's worth noting that some extended warranty covers the electrical batteries. If you are really going to become using the battery heavily (see the previous paragraph), this is really worth taking into consideration when the colored shirt guy at Buy More offers you an extended warranty at the time of the laptop expenditure. Find out if the battery is covered, and if your use pattern is such that you can be going through rather than the initial battery over the course of the extended warranty, maybe you are living in one of those situations in which an extended warranty really does make sense.