I purchased a "dead" original non-backlight Portable a month ago but have only had time to try it out today. When first powered up by me, using the Portable external psu, it displayed a sad Mac code that I have since interpreted as "power manager error". Subsequently, I have stripped and cleaned the box, and then tried to revive the battery using a generic Powerbook supply (loads of links but no real information: "Battery Technology" MC-0732). Alas I didn't measure the voltage before charging but after two hours, the battery showed 3.82V. After another two hours it fell to 3.52 V. And after another two hours, it is down to 3.22V (when I stopped).
Is anyone familiar with lead-acid batteries sufficiently to suggest a charging regime that might bring this thing to life? 6V motorcycle battery charger on trickle?