A lit charge/test light means the flash appears charged, so it’s probably not just draining batteries after two shots. Based on the troubleshooting suggested, check these possibilities:

• Press the flash’s test button. If it won’t fire from the test button, the problem is likely in the flash itself.
• Try the camera’s built-in flash. If the built-in flash works, that points more toward the external flash or its connection.
• Make sure your shutter speed is not above the camera’s flash sync speed, which can prevent normal flash use.
• In some shooting situations, the camera may decide flash isn’t needed depending on exposure settings.
• Overheating protection can stop firing, though that seems less likely after only two shots.

Since it works briefly after sitting overnight, that suggests either a flash fault, a protection shutdown, or a communication issue rather than normal battery use. Testing the flash with its test button and comparing it to the built-in flash are the best first steps.