Is it bad that I usually let my laptop battery die in the middle of work?

Bad for software: unsaved and corrupted data if it doesn't automatically sleep/hibernate when the battery reaches a critical level. In the worst case you may have to check disk or even reinstall your operating system (though Windows does try its best to prevent that even in the case of chronic unexpected shutdowns)

Bad for productivity: you may lose part of your work this way.

Bad for the battery: deep discharges generally are not beneficial for Li-Ion batteries (plus the charge/discharge cycles). It will wear out faster than for those who take better care of it (although it isn't as good for me either, who always keeps the laptop plugged in and cannot remove the battery; trickle charges plus the fact that it stays basically unused, fully charged and that also makes it suboptimal)

Other hardware though is unaffected (or not enough to change its lifetime significantly; maybe one to two days in 5 or 10 years)

How do I recalibrate a laptop battery?

It is a very simple process to recalibrate your laptop battery. Just follow the steps in order below:

1. Charge laptop battery to 100% or FULL.
2. Unplug the charger and let the battery drain till 10%.In control panel->power settings->check the settings to normal and remove all battery savings options you have selected.
3. When at 10%close all apps you were running.
4. Let the computer disharge by itself to 0%.
5. In unplug condition, at 0%,press the power button until the laptop the laptop doesn't start. (5–6 times would be enough).
6. Now charge the laptop the time it takes to charge completely. (DO NOT POWER ON).
7. If you don't know the time then charge it for 4 hrs.
8. Then switch on your laptop.

Your laptop battery is calibrated or rather RECALIBRATED

Can I replace 18650 cells in a laptop battery with a higher capacity?

The short answer is technically yes, mAh only refers to power capacity and how many milliamps the laptop battery can deliver per hour. The more important compatibility measurement is the voltage it supplies. As long as the voltage is close it should work.

Most laptop battery makers advertise their batteries power capacity in terms of 4400, 5200, 5600 or 5800 mAh. The basic idea is that 5800 mAh battery pack will allow your laptop to run longer than a battery with a 4400 mAh rating. Generally speaking this is true, but it is not the whole story.

Lets say your laptop need 20 watts of energy to run per hour. A battery pack that stores 60 WH (watt hours) will provide you 3 hours of run time. So where does mAh fit in to this equation then?

Answer: millamps(mAh) x voltage (V) = watt hours (WH)

Example 1: 2200 mAh x 14.8 V = 32.56 WH (theoretically around 1.5 hours)

Example 2: 5200 mAh x 14.8 V = 76.96 WH (theoretically around 4.0 hours)

But lots of other factor will play in as well, for example the type of usage, application being used? If you’re playing games, let’s just assume that the run time will be lower.