WARNING: Battery saving mode is on

[[Unknown]]

The warning is just telling you that battery saving mode is on. The actual battery saving mode is in your system settings somewhere. It means -

1. You have power/battery saving enabled on a Galaxy or HTC device. Turn it off.
2. You have battery saving enabled on a newer Lollipop or higher device. This is usually pretty obvious. Switch it off.
3. You have less than 20% battery power remaining. Charge your device.

PPSSPP is actually not doing much differently. Inside PPSSPP, the detection of power saving mode affects exactly two things:

A. It shows a notice so you can know to go into your phone's settings and disable it.
B. If you report game compatibility, it skips calculating a CRC of your ISO.

PPSSPP doesn't intentionally slow down when battery saving is enabled. However, your operating system does do this and PPSSPP can't make it stop.

-[Unknown]