If lithium power banks lack charge, it would help to know how long you need to operate for. Given the current you need (ideally measured with an ammeter, although you could take published currents for each of the parts of your system) and duration, multiply the time by the current to get a rough estimate of how much energy you need (in Ah).
For example if your system is taking 0.5A and you want it to last a day then you need 0.5 x 24 = 12Ah. (I'm not suggesting you need 0.5A, but I don't know how much current you do need)
My guess if lithium power packs is not enough is that you are looking for quite a lot of energy. One option would then be a 12V lead acid battery plus a 12V USB adaptor (readily available for car cigarette lighters or as bare PCBs). You could use a car battery (although they don't really like being discharged) or better one designed for deep cycle discharge (but they are probably more expensive).
An improved answer would be possible once the energy requirements are known.