DOS 3.2 or higher is required. (to support the 720K floppy)

Floppy Drive
  It's a 3.5" 720K Toshiba 4452A0P11 with a 34 pin edgecard connector. Both floppy drives are jumpered DS1

From Don Hills
   There were 2 models of floppy drive: Toshiba and Alps. The Toshiba used a metal band to drive the heads up and down, the Alps used a leadscrew. The leadscrew model could not step the heads at the full stepping rate of most PCs, so the stepping rate was set slightly slower in the BIOS. Trouble was, the metal band type drive was designed for full speed, and was very noisy when seeking at the slower speed. I wrote a small driver that loaded (and unloaded again) during boot to reset the step speed on machines with the faster drives. The drives looked identical externally, you had to look in the slot or remove them from the case to see the difference.

From Don Hills
   I was one of those guys. If you couldn't get the "sub C" cells, the trick was to use standard C size cells and duct tape them into a pack the same shape as the original. This "naked" pack fitted in the same space as the original pack-plus-case. The battery compartment was all plastic so the new pack was well protected.

   As for the power supply, as I said in an earlier post there was a US-only 110V "wall wart" that was only powerful enough to charge the battery when the system wasn't running. There was also a universal (100 to 240 volts) power "brick" much like those used on modern laptops, that provided enough power (15 volts DC, 2.7 amps) to run the system and all accessories while charging the battery.

The plug is the type that has a metal outer barrel as one contact and a metal-lined hole down the middle (Center positive)  that is the other contact. Size: now pay attention here. 5.5 mm external diameter, 2.5 mm internal diameter. They also come in 2.1 mm internal diameter, so don't get
the wrong one.
 

BATTERY CHARGER (#4060): 
A 110-volt input feature designed to be used to charge the internal batteries of the system.  It does not provide sufficient power output to allow system operation while the batteries are being charged

AUTOMOBILE POWER ADAPTER (#4065): 
Designed to charge the system battery while allowing simultaneous use of the system  unit. The adapter attaches to the system unit and plugs into the cigarette lighter outlet in a vehicle with a 12 volt negative-ground electrical system.

Open the battery compartment door and remove the battery. This is important, as many parts of the machine such as the memory chips are permanently powered so long as the battery is charged. The battery catch is on the bottom of the plug (like a modular phone plug).

Open the display by pressing the two small grey buttons under the carrying handle at the front right and left corners of the case. If you don't use the catches, you might snap off one of the small retaining catches on the LCD screen bezel. Pivot the display backwards until it is just past vertical. Press on the front bottom (notice the neat-o vertical serrations?) of the plastic plate covering the front of the display's "neck" until the plate pivots away from the neck, then lift the display up (wiggle it slightly side-to-side). This feature is why it's called the "Convertible".

Undo the 4 screws on the rear of the case. Lift and remove the rear (non pivoting) part of the top cover.

Pull the grey carrying handle forward, exposing 2 small slots in the case. Use a small screwdriver or coin to press inside the slots while lifting up on the front of the keyboard. Be careful not to damage the foil cable. Don't try unplugging it yet, just move it forwards and lay it on the extended handle.
Note that the keyboard pivots on two small hinges at the front of the lower case.

Undo the 4 screws holding the diskette drives in and pull the drives out. Thumb in the diskette slot, fingers underneath is the best grip. Note that the floppy drive bezels have catches that fasten them to the drives. They are not loose!

Reach in through the diskette drive bays with one hand and through the opening at the rear with the other, and unclip the diskette drive plugs from the clips on the underside of the (pivoting) top cover.

Lift the rear of the pivoting top cover and slide it forwards until the pivot pin at the front disengages from the slot it slides in and lift the cover up and away, unplugging the foil cable to the LCD socket as you do so.

You can now unplug the keyboard cable.

Reassembly is the reverse of the above, just 3 tricks:

When screwing the diskette drives back in place, BE EXTREMELY GENTLE. The screws must not be tightened too much- you will crack the drive front plates and/or break the plastic pillars that the screws go into. THEY ARE VERY FRAGILE. (Ed. They were cracked on mine)

I found that getting the LCD unit back on was interesting. Note that the LCD swings on a "trapeeze" that has a metal pin going through it. Note the two ptllars that come up on each side of the floppy and LCD headers. Notice the arc made by the top of those pillars. See the groove? Notice that the open end is toward the front.
   What I did- lower the LCD neck to about halfway forward. This lowers the cross-pin. Looking from the back, directly over the battery well, you can see the shaft AND the grooves. Now you can actually SEE how to position the top so the shaft will slide into the grooves.

When replacing the keyboard in its well, make sure the edge nearest the diskette drives sits on (not under) the small ledges moulded in the front plates of the diskette drives. These ledges lift the keyboard to typing position when the case is opened. If you get it wrong you may break things
when you try to close the case.  The front corners of the keyboard have little pivots that mate with the front of the bottom case. I had ot push down lightly to make them "snap" in place.

As for piggyback accessories, there were several. They were known as "slices", because they were the same profile as the back of the machine and when clipped on looked like an extension of the machine.

A few additions to your page:
There was no way of powering the system off completely without removing the battery. Some parts of the system, including the memory and much of the planar, were continuously powered. Being static CMOS logic, they consumed negligible power when not being clocked. The battery would hold the memory (and run the clock, there was no separate clock battery) for a couple of
weeks. There was no suitable CMOS diskette controller chip so it used a standard NEC 765. This was power hungry so was actually powered off when not in use- the BIOS saved and loaded the controller's state between drive accesses. I've got a lot more somewhere, including info gleaned from conversations with the actual developers, and the full IBM Tech Ref and
Hardware Maintenance Manuals.
 

5140 System Unit Options:
o   128Kb Memory Card (#4005)
o   Printer (#4010)
o   Serial/Parallel Adapter (#4015)
o   CRT Display Adapter (#4020)
o   Internal Modem (#4025)
o   Printer Cable (#4055)
o   Battery Charger (#4060)
o   Automobile Power Adapter (#4065)
       Optional Displays:
o   IBM 5144 PC Convertible Monochrome Display Model 1
o   IBM 5145 PC Convertible Color Display Model 1

DESCRIPTION
       The 5140 is available in two models. The model 2 is equipped with a CMOS 80C88 microprocessor, 64Kb ROM, 256Kb RAM, an 80-column by 25-line detachable liquid crystal display, two 3.5-inch diskette drives, a 78-key keyboard, an AC adapter, and a battery pack. Also included are an Application Selector, SystemApps, Tools, Exploring the IBM PC Convertible, and Diagnostics.
       The model 22 is the same as the model 2 with Diagnostics only. Both systems can be expanded to a maximum of 512Kb RAM via 128Kb RAM memory card features, and may include an asynchronous modem in the system unit.
       The IBM PC Convertible Model 003 with a Backlit LCD has internal illumination, which means it can be used in low-light conditions.  Battery life is dependent on the setting of the 
brightness control.  The Backlit LCD works on all PC Convertible models by plugging it into the LCD assembly, in place of the current screen, and installing the new power supply.  A new power supply is packaged with the Backlit LCD Option Kit.
       At the back of each system unit is an extendable bus interface.  This 72-pin connector allows any or all of the following options to attach to the base unit: Printer, Serial/Parallel Adapter, and CRT Display Adapter. Each of these features is powered from the system unit. The CRT Display Adapter operates only when the system is powered from a standard AC Adapter. A separate CRT display or television set attached via the CRT Display Adapter requires a separate AC power source.
       Each system unit is furnished with a detachable liquid crystal display (LCD). When latched in its closed position, it forms the cover for the keyboard and diskette drives. The LCD is attached via a "quick disconnect" connector, which affords easy removal so that the 5140 System Unit may be placed below an optional IBM 5144 PC Convertible Monochrome Display or an optional IBM 5145 PC Convertible Color Display.

128KB MEMORY CARD (#4005): 
 Expands the base memory of the system unit. Maximum: Two, for a system unit total of 512Kb.
Oh? I have a 5140 that had four memory cards in it. Go figure. The case has catches molded in for four of the memory cards.

From Don Hills
   System memory was 640 KB maximum, not 512 KB. There were 256 KB as well as 128 KB memory cards. Any combination could be used up to 640 KB. 256 KB cards were rare, what several people did was build a short ribbon cable to extend the last card's end connector to another 128KB card which they laid on top of the others under the keyboard. Space was too tight for my liking, so in my machine I actually ran the ribbon cable through to the modem slot and put the 5th card there. One of my later machines had 256 KB cards. They were easily recognisble as they had fewer (but higher capacity) chips than the 128 KB cards.

PRINTER (#4010): 
Attaches to the back of the system unit, or to an optional printer attachment cable for adjacent printer operation. It is an intelligent microprocessor-based, 40 cps (burst rate) serial, non-impact dot matrix design capable of low power operation. It draws its power and control from the system unit.  Standard ASCII 96-character, upper-case and lower-case character sets are printed
using a high-resolution, 24-element print head.  An all-points-addressable (APA) print mode for graphics is also provided. Near-letter-quality printing can be accomplished using either a thermal transfer ribbon on smooth (60 Sheffield units, maximum) paper, or no ribbon on heat-sensitive thermal paper. Draft-quality printing may be achieved using the thermal transfer ribbon on IBM Multi-System Paper (P/N 7034548) or equivalent.

SERIAL/PARALLEL ADAPTER (#4015): 
Attaches to the back of the system unit, Printer (#4010), or another feature module that might be
attached to the back of the system unit. The adapter provides an RS-232C asynchronous communications interface and a parallel printer interface that are compatible with the IBM Personal Computer Asynchronous Communications Adapter and the IBM Personal Computer
Parallel Printer Adapter. Looks like this

CRT DISPLAY ADAPTER (#4020): 
Attaches to the back of the system unit, Printer (#4010), or other feature module attached to the back of the system unit. It allows the user the option of connecting a separate CRT display to the system. The optional 5144 PC Convertible Monochrome Display or 5145 PC Convertible Color Display may be attached via this adapter. Through the use of optional connectors or cables, the CRT Display Adapter (#4020) also allows the attachment of the IBM 4863 PCjr Color Display, IBM 5153 Color Display, or a standard television set.

LCD Display
From Don Hills
   The original systems had a first generation LCD display- my first machine came with one. These were grey and low contrast. They were upgraded with a supertwist LCD (sort of green/navy blue) that had much better contrast. My first machine came bundled with this upgrade which I performed myself. I only ever saw one system with the backlit LCD. It used an electroluminescent
panel rather than a fluorescent tube and diffuser. They fell out of favour because they couldn't produce as much light as a tube. The backlit LCD was OK in very poor light conditions, but in normal room lighting or sunlight you were much better off with the standard supertwist. I used to sit up in bed writing code (DOS device drivers in ASM, for example) with my machine. I had a small lamp mounted on the wall behind me that shone at just the right angle for good visibility. The display characters were large, and it was easy to load different fonts into the font memory until you found one you liked.

INTERNAL MODEM (#4025): 
Provides the user the capability to communicate with other compatible units/systems over existing telephone lines. It uses modulation methods and frequency tolerances equivalent to either Bell 212A (1,200 baud) in high-speed mode or Bell 103A (300 baud) in low-speed mode. It is offered as a complete assembly consisting of two cards connected by a cable. The entire assembly is installed in the system unit.

IBM 5140 AP Internal Modem Connector Pinout 
Thanks, Peter!

 I/O Pin  Signal Name               I / O 
   01     + Adress/Data Bit 0        I/O 
   02     + Adress/Data Bit 1        I/O 
   03     + Adress/Data Bit 2        I/O 
   04     + Adress/Data Bit 3        I/O 
   05     + Adress/Data Bit 4        I/O 
   06     + Adress/Data Bit 5        I/O 
   07     + Adress/Data Bit 6        I/O 
   08     + Adress/Data Bit 7        I/O 
   09     + Adress Bit 8             I 
   10     + Adress Bit 9             I 
   11     + Interupt Request 4       O 
   12     - I/O Read                 I 
   13     + Reset                    I 
   14     - Data Enable              I 
   15     Ground                     GND 
   16     + Adress Latch Enable      I 
   17     Ground                     GND 
   18     + Adress Enable            I 
   19     Ground                     GND 
   20     + 12 VDC                   PWR 
   21     Ground                     GND 
   22     Ground                     GND 
   23     Ground                     GND 
   24     Ground                     GND 
   25     - 13 VDC                   PWR 
   26     Ground                     GND 
   27     - I/O Write                I 
   28     + 5 VDC                    PWR 
   29     Ground                     GND 
   30     + High Z                   I 

PRINTER CABLE (#4055): 
A cabling accessory 22 inches (0.6 meter) in length with a custom 72-pin system-type connector attached to each end. It provides the user the option of operating the Printer (#4010) immediately adjacent to (that is, physically detached from) the system unit, to provide flexibility of placement for ease-of-use and visibility.
.
Mad Max has one of these, looks like THIS

IBM 5144 PC CONVERTIBLE MONOCHROME DISPLAY MODEL 1
       The 5144 Display is a 9-inch (measured diagonally) composite video display that is attached to the system unit via the CRT Display Adapter. The display stand, an AC power cord, and a signal cable that connects the 5144 to the CRT Display Adapter are provided with the 5144.  Character box size is 8 x 8 pels. Text modes are 80 x 25 and 40 x 25. Graphics modes are 640 x 200 and 320 x 200.

IBM 5145 PC CONVERTIBLE COLOR DISPLAY MODEL 1
       The 5145 is a 13-inch (measured diagonally) color display that displays in medium resolution (320 x 200). It is designed for those customers whose application requirements will be satisfied by that resolution. It is attached to the system unit via the CRT Display Adapter (#4020).  The display stand, an AC power cord, and a signal cable that connects the 5145 to the CRT Display Adapter are provided with the 5145.  The display includes a speaker for external audio output. The 5145 will display business and graphics data in 40 x 25 character mode. In 80 x 25 character mode, the 5145 can be used for word processing and text applications.

ACCESSORIES
CARRYING CASES: Two soft-sided carrying cases are offered for the IBM PC Convertible.  The standard model (#4090) will accommodate the system unit, system-attached printer, various accessories, and supplies.  The system unit and printer can be operated from within the case.  The compact model (#4095) may be carried by hand, worn over the shoulder, or carried backpack style. This model holds the system unit in the main compartment and has an expandable pocket
where the printer, accessories, and paper or a notebook may be stored.
SUPPORTED OPTIONS:
o   IBM 5153 Color Display
o   IBM PCjr Adapter Cable for the IBM Color Display (#0021)
o   IBM 4863 PCjr Color Display
o   IBM PCjr Connector for TV (#0020)
o   IBM Communications Adapter Cable (#2067)
o   IBM Proprinter (#4201)
o   IBM Graphics Printer
o   IBM 3708 Network Control Unit
o   IBM 3710 Communication Adapter
o   IBM Personal Computer Printer Cable
o   IBM 5841 Modem - 1200 bps
       All IBM Personal Computer, IBM PCjr, IBM Personal Computer XT, IBM Personal Computer AT, or IBM Portable Personal Computer options, adapters, and devices not specifically listed above have not been tested on the IBM PC Convertible System and are not supported.