I'm sorry, but it's not possible to replace the "My battery is low" audio file on the IoTiny. The audio messages are hard-coded into the firmware and cannot be changed by users. The IoTiny does not have user-accessible flashable memory where these files are stored. The only way to change the audio messages would be to modify the firmware, which is not something that Synthiam supports or recommends.

I remember my AdventureBot was having really bad battery issues around 2016. It wouldn't charge. Since I was a little kid, I was worried that it would get angry at me. I did replace the battery about a few weeks later.