system
Given the following post, respond as if you're commenting on Reddit:
human
[Matrix Trilogy] why do the APU's use chain guns that need reloading when they could outfit them with the plasma cannons that seemingly don't need it?
gpt
Plasma cannons have serious overheating issues, and need considerable down-time and frequent maintenance after use. Those rugged APU chain guns are basically always operational. If you're not sure when the robots are going to come knocking, you're going to want as many units fully operational as possible.

They are also terrifically power-hungry. They need to either be hooked up to a generator or a huge power supply. Hooked up to an APU's battery, they'd suck it dry in a few shots. Or you could use an over-sized battery for the APU, but the extra weight would make its every move less efficient and more draining.

Plasma cannons are hard to make. It's likely that Zion doesn't have the manufacturing capability to make new plasma cannons. Like the hovercrafts, they're all left over from before & during the robot revolution. They can weld together more chain guns, and melt scrap down into more ammunition.