My watch have been doing this lately. After a few minutes, it goes back to normal, the weird part is that the battery is fully charged, I use it outdoor every day.
How to tell if the battery is about to Drain on a Gshock? | WatchUSeek Watch Forums
How Long To Charge A Casio Solar G-Shock From Medium To High | BestWatchBrandsHQ
Casio G-Shock Battery Life - All You Need To Know [Field Tested] | SurvivalMag
Power Levels
Amazon.com: Casio Men's AL180AMVV-1 Tough Solar Digital Sports Watch : Clothing, Shoes & Jewelry
How Long To Charge A Casio Solar G-Shock From Medium To High | BestWatchBrandsHQ
Casio G-Shock Secret Features and Hidden Screens — 60Clicks
Got this GShock GW-M5600 since 2008. Battery went to low only once after I started getting into Seikos. It's my time reference when I set my automatic watches :) : r/BuyItForLife