The battery is a CR2025 
If anyone has suggestions for alternative to this product that is easy to replace and maintain I would be interested to hear about it.

I closed it with super glue.
Replace with CR2025
| I was able to open the casing with thumbnails on either side | 
| The tile opens into three pieces and contains a CR2025 battery | 
| The battery is glued down so I needed to work it out with a box cutter. | 
| The battery sicks to the blade | 
I closed it with super glue.
Replace with CR2025