External battery for HP Prime?

[grsbanks]

The Prime itself is designed to accept 5V because it connects to a USB port.

Power packs that provide USB ports for charging output 5V even if the battery inside them is only a 3.7V battery. There's a DC/DC converter that steps that up to the required 5V.

Chargers and power packs that say that they output, for example, 3A don't force that level of power through their load. It just means that they can provide up to 3A if you ask it of them.

Depending on what the Prime actually draws, a power pack will or will not work. Most devices being charged switch the charge to a very low level called "trickle" charge once their battery is full. Power packs detect this much reduced load and switch themselves off when that happens. The question is whether the normal charging current of the Prime is sufficient for the power pack not to think that it's gone into trickle charge mode and there's only one way for you to find that out. Try it!

No damage will be done to your Prime unless the power pack develops a fault and somehow blasts far too many volts down the pipe (unlikely, these things tend to just go dead if they go wrong). If that happens then the warranty on your Prime will be void because you were using a non-HP charger.