For me, the battery indicator is not that great on any vape I've owned. On the vapes where I can remove the battery to charge, the nightcore always seems to indicate a bit more than I'd expect left based on the indicator. The IQ, with all its bells and whistles, is no better.
As to the "overheating", it is a hot vape. I've heard using lower amp batteries will help with that, but I've not found that to be true to any marked extent.
I'm not sure either reason is a defect in the product that gives full right to return to davinci. (If another seller, your remedies are there.) If you do have rights to return under the seller's return policy, I'd bet your unit is operating pretty much as most of them would without defect, so would return without trying too much else.