So excited for this device!
Looking forward to the release.
As the battery has the same capacity and the rk3399 uses more power than the A64, you can expect less time on a full charge.
However, they use a special rk3399 designed for the phone, called rk3399s, which is a bit undervolted. This makes it run cooler and use less power than a normal rk3399.
But currently, not much software optimization has been done for this, so my guess would be about 8-10 hours of usage, on medium to light load at this point.
This will ofcourse be improved, when we actually get suspend working.