MacBook Pro will not power on or charge after RAM upgrade.

In principle nothing should go wrong with a simple RAM replacement, especially when one puts utmost care by wearing a wrist wrap. Since you disconnected battery, double check the small battery indicator cable sitting beside battery is correctly in place. Try starting your Mac without the small connector and battery disconnected too. Double check all cables connecting to the logic board are firmly in place. That’s about all you can do..if nothing works it might be either an unlucky coincidence or an incident, but would need some board testing to get further.