Is the speaker still charging when in use?
Don’t know what model or type you’re referring to but usually if the charging current is higher than whats being used, then the extra is used to charge the battery. But every device is different, there are some where you can’t use the device while its charged or something like that.
Generally, the speaker will still charge, but at a slower rate. This is OK to do once in awhile, but the simultaneous charging and discharging can “stress” the battery and possibly degrade its performance over time.