The battery, memory, and drive bays are meant to be accessible to end users. Swapping their contents won't void warranty unless you plug something inside which is electrically incompatible.
It's good practice to disconnect all power sources before servicing components - unplug the adapter, remove the battery. It's good practice to unplug power connectors before unplugging signal connectors, then plug power connectors after (re)plugging signal connectors - just another way to ensure your fragile logic boards and NV flash aren't exposed to momentary voltage spikes. And it's good practice to use proper ESD protection when working with sensitive electronics. But it's not strictly necessary because the laptop charging circuitry contains failsafe power isolation/buffers, and most other PC components (like the mainboard and even SSDs) have onboard VRMs hardened by power diodes and capacitor banks at the most critical areas.
"All opinions are not equal. Some are a very great deal more robust, sophisticated and well supported in logic and argument than others." - Douglas Adams
[/Korth]
