Panasonic CR2016 3.0 Volt Long Lasting Lithium Coin Cell Batteries in Child Resistant, Standards Based Packaging, 2-Battery Pack

Your watch appears to be a 2004 Timex Indiglo Quartz reference 24421. This model is shown in the Timex website archive here. The instruction manual is available here. It uses a standard CR2016 3.0 volt lithium coin cell battery. The date code M2 on the back of the watch indicates yours was manufactured in February 2004 according to the table here. Hope this helps a bit.