I have laptop (Acer Aspire 7745G) which has charger 19V-4.74A and battery 11.1V - 6,6Ah (73Wh). I'm planning to buy powerbank for it but I don't know what voltage would be okay. I'm looking to this powerbank I see that it has DC output of 12/15/19V. So, can I use this powerbank for my laptop? If yes, what voltage of output should I use?
You almost certainly will not be able to replace a specific laptop's battery with a "power bank". The motherboard will not recognize the power bank as a valid battery, so it will not attempt to charge it. There is a communications protocol between the motherboard and the battery, and the exact nature of the messages is usually not public.