I have a TRS 80 Model 100 and while doing a routine maintenance. I noticed the internal NiCad is showing sign of crystal forming. Before allowing it to leak and destroying the PCB, I ordered a 3.6V 60mA NiCad replacement from eBay to replace it.
I was planning to remove PCB to do it properly, however after the cover was removed. It seem like it can be done without removing the PCB.
Using the 40W solder iron, I heated each leg of the NiCad battery from the top side and gently removing each leg. Then I used the solder wick to clean up the solder points and install the new battery in it place. Afterward, re-solder each leg with sufficient heat to ensure proper bonding.
Once everything is put back together, hook it up to external power adapter and let it charge. Now unless, one of these electrolytic capacitors start failing. It should extend the life of this laptop another 5+ years.