And well you should be. That's no doubt the total current capacity of all the 18650s or whatever are inside. At 3.6 Volts. Getting that to 12 will probably cost you something over 300%, that is one Ah will cost you 4 Ah of battery. If they're honest.
Another way to do it is to put 3 in series for 15 Volts total. The 'five volt only' ones are cheaper and probably more efficient at that single voltage (variable voltages are more of a compromise to cover the range).
OTOH my solution to this is sitting in front of my 'Solo warbag'.
3 protected 18650s in series, works great, simple. Normally it lives in a side pocket in the camera case. I made up several, AFAIK they all found happy homes. Somebody with ambition, modest soldering skills, some free time and a sense of adventure should make some?
OF