Make sure you measure the correct way: connect the poles to their corresponding measuring ends.

Mixing batteries causes an imbalance in the energy flow. Some batteries will overcompensate this by discharging faster than usual - greatly reducing their lifespan.

Don’t charge an alkaline or zinc-carbon battery, they are not designed to be charged.

Expiry date indicates how long the battery will function properly according to industry standards.

This is a vibration noise which occurs when electric current flows through a transformer or a winding wire inside a component part. However, the charger may still be used without any concern as there is no need to worry from a safety point of view.

Turn off the device and remove the battery immediately. Remove the remaining leakage using a cotton swab. Avoid skin contact at all times.

Batteries are best stored at room temperature. Extreme heat or cold can significantly reduce battery life.

Always insert batteries with the poles in the correct direction. Not doing so will lead to a short circuit.

The revised RoHS (Reduction of Hazardous Substances) Directive 2011/65/EU...

Perhaps you are using a different battery type. Zinc carbon will perform otherwise compared to alkaline, for example.