I have a Alcatel Pixi 4 (4"), model 4034E, and I noticed that when I watch a video using Opera the CPU increases, as expected. However, after I finished watching it, the CPU may not reduces the usage, keeping whatever usage it had while playing.
Example: if to play a video Opera needed 50% of CPU, if I change the open application or after I finished watching and closed Opera, it still uses 50% of CPU. Consequently this causes heat and drains battery quickly.
This is not something consistent, as this doesn't always happen and I don't know what triggers it, but I have seen this happening only with Opera.
The workaround I have found to reduce the CPU usage after watching a video in Opera is to open a media file on the Chrome browser. As the base is (apparently) the same for both browsers, somehow Chrome solves the problem Opera causes. It doesn't work 100% of times, but after a few attempts this work.
Opera version is 44.1.2246.123029