The results of a voltmeter vary depending on the type of voltmeter used. For a more accurate result, be sure to use a voltmeter with more than 1 megaohm input resistance for alkaline buttons batteries or a 10+ megaohm for lithium batteries.
Batteries in smart keys usually last between 1 to 2 years. Unusually short battery life may be caused by electromagnetic interference. Avoid keeping your smart key near other electronic devices such as phones, laptops and other screens.
As zinc air hearing aid batteries operate differently than other batteries they have different characteristics. In winter, rooms may be drier, warmer or badly ventilated. These effects can disturb the performance of your batteries.