If the red indicator flashes slowly,which means the battery power is low (<15%,please kindly charge it as required), it will take about 5 hours to charge fully.

When the battery is low, the light flashes red. While it's charging, the light is solid red. When it's fully charged, it turns blue. The manufacturer's leaflet states the battery charge time is 5 hours and the music playing time is up to 24 hours.

Sorry you could not link two of them together at the same time.