TINY RTC 1307 pin batt question

Hello!!
anyone knows how to use the BATT pin and know the voltage on lithium battery?

best regards.

Can you please provide a link to the device ?

here is a photo to the device http://blog.simtronyx.de/wp-content/uploads/Tiny-RTC-DS1307-Echtzeituhr-Pinout-Rueckseite-blog.simtronyx.de_.jpg

Here is the photo with the battery, Lithium Ion 3.6V LIR2032

3V coin batteries CR1220 (12mm diameter) or CR2016/CR2032 (20mm diameter) work fine. They also last years (hence no need for the more expensive rechargeables).