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.
Casio Men's G-Shock Stainless Steel Tough Solar Atomic Digital Watch MTGM900DA-8 - Walmart.com
Casio G-Shock Battery Life - All You Need To Know [Field Tested] | SurvivalMag
Men's Casio Tough Solar Power Sports Watch STLS100H-1AV
Solar-powered - Collection - EDIFICE Mens Watches - CASIO
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