so I just upgraded to a P4 and I would like a extra battery. So my question is should I buy a used battery ? Or should I buy a new battery ? I was in a hobby shop and they told me about 80% of things that go wrong with DJI are battery related so I should always by New when it comes to the battery. ( he was maybe just trying to make a sale ) but has anyone heard this before? Or what's your take on new or used batteries?