The HP Stream 7 has a terrible battery life. Reports on forums indicate that it is due to the connected standby mode in Windows 8.1 and also the Intel SST Audio driver. The combination of these two factors means that approximately 2-3% of battery is drained per hour as your tablet is not able to fully sleep. Typically, my tablet wakes up flat in a couple of days. That sucks.
The simple workaround is to lower the tablets volume to “0” with the volume rocker before putting your tablet to sleep and also switching Wi-Fi to off. This will improve the standby battery life from hours to days. However, this is a tedious process.