Kinda. Battery life will be worse though. Tablet has a larger battery as there is more space, dumbphone has longer battery life because it uses so little power. It will be far more powerful than the tablet and with fdroid I can install pretty much everything I need. Family like to message on whatsapp though, which is the only thing keeping me from immediately sticking PostmarketOS on it which I have used before on a Pinephone.

Do wish that larger powerbanks were more common. ~74Wh (20,000mAh at 3.7v) seem to be one of the cheapest per capacity available and I suspect it is because of mass production. Larger are usually more like camping batteries and cost more, I suspect because they don't sell as many of them. Cheapest per Wh for larger capacities is probably best achieved by just sticking multiple together.