How far down does it get ?
A bad battery will usually get down to around 11.2 volts while just sitting, that is a bad cell.
If it continues down below 10 volts you have a parasitic drain on your system, that is something is draining the power while the bike is stopped.
Are you 100% sure you are not turning your parking lights on ?
Are you battery cables clean and tight ?
What aftermarket stuff do have fitted ?
A bad regulator can cause a drain but I have never heard of this on a Strom.
With the bike shut down remove the positive battery cable then put a AMP meter between the positive battery terminal and the positive cable, take a reading it should be very very low something like 0.003amps, if it is much bigger you need to find the source of the power drain.
Some of the 19 rides in my shed
2014 V2, Snoopy
2009 Wee, Pumbaa the pig
WR450F, The Blue Postie Bike
YZ250N smoker with rego, Stinky.
Yamaha MT09 (FZ09), The Scud missile.
Club Lead not Club Med.
He with the most toys wins.
Out of my depth in a puddle.
Live life on the edge you will see more that way.
Ridding a motorcycle keeps things in balance.
At the end of each trail and at the end of each day history is made.