I have been riding with the BV6000 full brightness for 4 hours and consumed only 45% of the battery. So when I compare the BV6000 to your phone, your screen is bigger so I assume it requires more energy and your battery is much smaller.
So if you want to keep the HTC and don't want to add an additional powerpack, I think you can only try to reduce your brightness setting or configure BLEvo in such way that the screen is not always on but only for example when you press the new remote.
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