[myself248]

That's unusual for modern machines. It was de rigeur from the first portables up to about 2005, as I recall.

I was rudely surprised by my first Core 2-era machine that wouldn't boot without a battery installed, because prior to that, from Pentium-based Toughbooks back to the 486-based Noteflex back to various 8088 and even pre-x86 machines (PC8201A, club100 represent!), they were all absolutely fine running from the power inlet alone with no battery.

The Zenith MiniSport was the sole exception because the power jack was actually physically on the battery, but you could still gut an old dead battery and make a dummy, and it would run from the brick just fine. (This is documented in the very first issue of Brian Mork's excellent Minisport Laptop Hacker zine, available wherever fine textfiles are sold.)