Battery:        

                 https://play.google.com/store/apps/details?id=com.ijinshan.kbatterydoctor_en&hl=en

Battery Saver:      

                https://play.google.com/store/apps/details?id=com.dianxinos.dxbs&hl=en

Hardware Tester:  

                https://play.google.com/store/apps/details?id=com.antutu.tester&hl=en 
Audio Test:  

               https://play.google.com/store/apps/details?id=de.guentherkrauss.audio.audiotesttonegenerator&hl=en
Video Test:

               https://play.google.com/store/apps/details?id=com.antutu.videobench&hl=en

Benchmark:

              https://play.google.com/store/apps/details?id=com.antutu.ABenchMark&hl=en

Wifi / Speedtest:

             https://play.google.com/store/apps/details?id=org.zwanoo.android.speedtest&hl=en
Wifi Signal Strength:

            https://play.google.com/store/apps/details?id=com.northbridge.wifisignalstrength&hl=en