It's not the battery, it's the stator you need to think about. And it's not volts, its amps that are the killer.
The problem comes if the current drawn your stuff adds up to more than the current the stator can provide. If this is the case and you're lucky, the current deficit will be made up by the battery. The battery will go flat and when you next stop you won't be able to start. But if this is the case and you're unlucky, the stator will try harder and harder to produced meet the demand for amps and it will burn its little coils out.
You need to know how much current in amps the stator can deliver. Should be in the handbook, but if not then a forum somewhere. Then tot up the amps drawn by the headlamps on full beam + rear lamp + grips + power pack/mobile*. If you don't know the amps, then take the power rating (in watts) and divide by 14. If the stator can deliver what's needed, then you're ok. If not, you still might be able to swing it by juggling your accessories, e.g. by only having the grips on low if you're charging the power pack. Or if not, you might be able to swap the headlamp bulbs for LEDs.
*The sat nav is probably too small to bother about, and the brake lights and indicators aren't on long enough to make a difference (because the electric can overdeliver amps for short periods)
Some bikes use some clever circuitry to cap the current available through a USB port at 1A or 2A - check in your handbook; if this is the case with yours, this will be the maximum current the power pack can draw, no matter what it would draw if it were connected to a mains transformer.