Replacing the batteries is a simple operation that does not affect the warranty in any way.
The batteries used are 2 alkaline type C - 1.5V LR14 , a type that can also be easily found in supermarkets.
Here are the steps to follow:
1. Turn the device SOLO upside down and unscrew the 4 screws using a Phillips screwdriver
2. Remove the cover. There's a rubber gasket between the two shells to prevent water from entering. To separate them, pry evenly from the four corners with a flat, rigid object, such as a flat-bladed screwdriver.
3. Remove the batteries
4. Wait at least a couple of hours
5. Insert the new batteries, orienting the positive (+) and negative (-) ends as indicated on the labels inside the compartment.
6. Perform a connection and/or opening test with the case still open
7. If the test is successful, close the cover and re-tighten the 4 screws on the back, being careful not to tighten too tightly.
Demo video: https://youtu.be/sv7pwPTfb6I