Are notebook batteries generally hot-swappable?

Best practice says no, but I used to do it all the time without any problem what so ever.... However, it really depends on the laptop - I have never had a problem, but, yours may have a very sensitive PSU and the change in power requirements could either restart or blow something.

If I was you, look up the cost of a replacement battery - you may be surprised, some are as cheap as $20, ask yourself is it really worth the trouble for that amount of money? Memory effect doesn't really exist any more and by the time you experience wear and tear on a battery, it will probably almost be time for a new laptop.

As other answerers have said, this is a very "your mileage may vary"-ish issue, dependent on your particular tech. But just to provide another viewpoint...

A few years ago, I bought a Fujitsu laptop that worked great for about a week. Then I popped out the battery just the way you said, and since then, the computer has only been able to last about three minutes without AC power, even on a fully charged battery. Either the computer is destroying good batteries that I put in, or the amount-of-juice-remaining sensor was permanently damaged; I never bothered to figure out which.

To add to what Wil already said. I also never had any problems with it. Yes, recommendation is not to do it, but then again, I've read some funky recommendations over the years, half of them probably useless.

As far as your laptop model goes, I have hp compaq 6715, which is relatively simlar (at least visually), and it never had any problems with that sort of thing.

If you're reading this, it worked. Things I've done:

• Removed battery while on battery dead condition and under AC power
  • Sleep remembered running programs as normal

And reversing polarity

• Put PC back to sleep mode to plug dead battery and under AC power
  • Sleep remembered running programs as normal

If you're not reading this I further destroyed my suspect battery.

Details:

• Win 8.1 x64 Lenovo Z40
• Battery: OEM Lenovo L12M4E01
• Battery wear level = 81% (according to 3rd party battery life software)(100% is new)