Unlike later portable computers from Apple and other manufacturers, the battery is charged in series with the supply of power to the computer. If the battery can no longer hold a charge, then the computer cannot run on AC power and hence it will not boot. The main reason for this is that the original power supply had a very low output. This is also why in many instances the special low-power hard drive would not spin up. Several popular unauthorized workarounds were devised, including to use the power supply from the PowerBook 100 Series which provides a higher output. As with automotive batteries, the sealed lead acid cells used in the Portable failed if they are fully discharged. The batteries are no longer manufactured and it is very rare to find an original battery that will hold charge and allow the computer to start. It is possible to repack the battery with new cells, or use alternative 6 V batteries . The sealed lead acid cells used in the Portable's battery pack were made by Gates and were also used in Quantum 1 battery packs for photographic flash use.
Despite the dramatic improvement in terms of ergonomics offered by the responsiveness, sharpness, and uniformity of its active matrix panel, one of the drawbacks of the Portable was poor readability in low light situations. Consequently, in February 1991, Apple introduced a backlit Macintosh Portable (model M5126). Along with the new screen, Apple changed the SRAM memory to less expensive and more power-hungry pseudo-SRAM (which reduced the total RAM expansion to 8 MB) and lowered the price. The backlight feature was a welcomed improvement, but it came with a sacrifice: battery life was cut in half. An upgrade kit was also offered for the earlier model as well, which plugged into the ROM expansion slot. The Portable was discontinued in October of the same year.
In addition, at 16 pounds (7.2 kilograms) and 4 inches (10 centimetres) thick, the Portable was a heavy and bulky portable computer. Lead-acid batteries, although providing long uptime, contributed to its weight and bulk.
Read more about this topic: Macintosh Portable
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