Some notes and lessons learned regarding the BP150 from my project of turning one into a wireless text terminal:
The Business Partner 150 is a close cousin to the Tandy 1100FD, 1110HD, and probably others. These machines all seem to have the same core characteristics (NEC V20 CPU, 640K RAM, etc) with some different peripherals (backlit or non-backlit display, hard drive or disk-on-chip, etc). They are similar to the point that you can mix and match some components (even motherboards, in my case) between them with a fair degree of success.
If you have one of these and the laptop won't turn on, even with the power supply functioning and plugged in, check the solid-state fuses on the motherboard. I've had two of this family of machines and each has blown at least one of the fuses on the motherboard. The photo at right shows the location of the fuses just behind and to the right of the power switch. In the photo I've already replaced two fuses with wires, only one remains.
At this point, the original battery in these machines is surely shot. I have not been able to find a drop-in replacement, but the Panasonic LC-R061R3P is only slightly larger than the original. I only had to cut away a little bit of the case's internal structure to make it fit. This batter has slightly less capacity than the original but was the best I could find. Googling "Tandy 1100FD battery" used to return several hits for merchants selling replacement batteries. The thing is, the original battery is a 6V lead-acid - but the replacements are all NiCds! That can't be right. If you see such a "replacement" advertised, proceed with caution.
If you have a completely dead battery but you really don't want to replace it, it is possible that the battery itself has some life left in it but another fuse has blown. There is another solid-state fuse within the battery pack that might be worthwhile to check. You'll have to cut off the outer plastic covering to get too it. (Be careful to not cut into the battery pack itself.)
The floppy drive is probably shot too. The original floppy drive used a belt to connect the motor to the spindle, and this belt stretches and degrades over time. You can replace the floppy drive with a standard 3.5" floppy drive, but it is a bit of a hassle electrically. Mechanically the replacement is simple -- the new drive should almost drop right in. I had to cut off a couple of plastic nubs on the inside of the laptop case, remove the floppy drive's face, and trim down the floppy drive's eject button a bit -- none of which was difficult. The difficult part is making the electrical interface to the laptop. The original floppy drive uses a flexcable which contains all the standard signals but uses its own pinout and I've never seen a floppy drive with a matching connector. The fix is to remove the flexcable connector from the busted original drive and solder up an adapter cable from that to a standard floppy drive connector. There's a paper by Ivan Baggett that describes the procedure better than I could. You can see a bit of my adapter cable in the above photo.
There's a 16C452 chip (or its relative) on the motherboard that handles two serial ports and the parallel port. The first serial port goes to the DB-9 connector on the back of the motherboard, the other one should go to the expansion connector (for an optional 2400 baud modem). For my project I cut the traces for the first serial port and wired the radiomodem to them. It would have made more sense to use the second port, since the port that actually goes to a standard connector is more likely to be useful for something else someday.
This may not be true for all versions of these laptops, but in mine the BIOS had at least 8K of unused space at the bottom of the BIOS EPROM. Very useful place to stash code if you don't want to have to use the floppy.
With one machine I had lots of trouble with certain keys not registering keystrokes. I spent lots of time troubleshooting the keyboard before I figured out that the keyboard was fine, the problem was instead with the chip on the motherboard that interfaces to the keyboard. That chip, unfortunately, is surface-mount and has no markings on it, so I don't see any hope of replacing it. Instead I found a Tandy 1110HD cheap on ebay and swapped motherboards.