Unless there's step up and step down regulation your device can only give you what volts are left in your battery. There are device's that have step up regulation like the DNA 20 or 30 but no step, to get both your have to look into the SX350 chip mods runs about $250.00 and up for pre-built device though you can build one yourself for under $100.00 it's not that hard they come pre wired your have to get a case and cutout the holes and battery holder.
DNA 20-30 step up regulation works like this, device will give you wattage based on volts of battery until the battery volts go below the wattage you set then it will regulate it at your settings.