2. The T1100 Maintence Manual indicates that the T1100 can be powered from the AC adapter ("quote: "And you can drive the T1100 by AC power through the AC Adaptor in an office."). Note however, that I have two T1100 units (T1100, not T1100 PLUS), and from experimentation, simply plugging in the T1100's AC adapter does not get around the problem of a missing or faulty battery.
Battery state
Minimum battery voltage
The battery needs to be sufficiently charged before the T1100 can power on. According to my experimentation, that corresponds to about 10V of battery voltage. However, because the battery is directly connected to the +12V line of the internal diskette drive, the drive may not operate correctly at that low voltage. So, 10V should only be considered as a minimum for the system board.
Note that the 'LOW BATT' light does not work if the battery voltage is less than about 10V.
Discharge
My experimentation shows that the 'LOW BATT' light turns on when the battery voltage drops below 11.9V
If the T1100 is further used, the T1100 will stop working altogether (including the 'LOW BATT' light) when the battery voltage drops below about 10V.
Battery charging
You recharge the internal battery via the AC adapter.
AC adapters
Page 1-6 of the T1100 Maintenance Manual indicates that the output of the AC adapter is 18V DC (supplying up to 600 mA of current).