The instrument can not be turned on / off normally

(1) Is the battery charge low? Please replace a new battery. (2) Is the battery positive and negative? Install the battery in the correct way. (3) Is the battery shrapnel bad? ① Please check the battery shrapnel is deformed, and the battery leakage is exposed to the shrapnel, resulting in shrapnel is oxidized, can not be normal conductive contact? ② Please use the appropriate tools to remove contaminants on the shavings and other oxides, and dipped in a little alcohol to dry and then into the battery. (4) Whether the key mask is broken or failed