It took me half a day to get mostly dead RTC and RAM backup batteries from two desktop and six notebook computers. In 50% of cases the batteries already started leaking so they would soon kill the computer.
I didn’t replace the batteries with new ones as I don’t need another ticking bomb in my old machines. Now I have to access BIOS setup every time I want to use the computer. That’s the only drawback but I can live with it.
We all have Lithium-based batteries in our mobile devices today. In mid-80s there was the first wave of battery-powered portable (IBM compatible) PCs. They used lead-acid batteries which are much heavier for the same charge capacity. There were a lot of troubles connected with these batteries. Average battery lifetime in a laptop was about one to two years before charge capacity degraded. If you discharged the battery too much or let the device unused for a longer time you had to replace the battery. You even had to unplug your device from wall power when the battery was full. Otherwise it can be damaged according to manufacturer’s instructions.
On the other side these batteries were (and are) cheaper than any other type suitable for large portable computers. These two were removed from my Bondwell Model-8 laptop. They are not specifically designed for the laptop so they can be easily replaced with new ones even today after 30 years. Similar ones are used in some devices such as emergency lights.