trettum,
Most power banks don’t like being charged while power is being drawn from them, so we don’t recommend doing so. Some in fact just won’t let you. I haven’t personally tried the PowerCore Slim 5000, so I can’t recommend it.
Edit: I just checked the Q & A on the PowerCore 5000 Spec Sheet (Q No.7) - Anker say they have specifically blocked the ability for this unit to power other devices while it is on charge ‘to protect external batteries’.
You would be better considering the Anker PowerCore 20100 - available from Amazon, which will power Rosetta for up to 18 hours between charges - so will easily cope with a full day’s flying. I have used these for almost 4 years now and still going strong, thoroughly recommended.
Best Regards
Peter