AccuBattery is an indispensable tool in case your phone runs out of battery very fast, but you can't find out the reason for it. The app allows to optimize the battery and displays detailed information on the loss of battery
Battery Doctor app helps you to optimize your battery performance by providing complete information on its consumption. It's a free program with no paid subscriptions. The only drawback is the presence of advertising
Disk Speed is a small but a very useful free utility for Android: it can show the current status of your sd card. In order to write and read data you can specify a) the entire storage device or b) its part.