I assume you checked the receiver battery with an expanded scale volt meter that applies a slight load? You may want to go even further and monitor the battery in action. Watch it while moving the controls for a while. Maybe even put a slight weight or other restriction on the surfaces to simulate actual flying conditions. Maybe you can catch the battery falling off under heavy load.

You may also want to check for voltage drop across the switch or connectors.

After an incident like you had, I personally wouldn't trust the battery, switch or receiver unless I found the exact cause.