Batteries usually lose their charge slowly, they just don’t quit working. A battery tester is the best way to show the condition of a battery. A good battery tester will tell you if a battery is good, ready to fail, or needs to be replaced. The most common home devices that use batteries are remote controls, flashlights, and automobile keyless entry devices.
When a battery operated device doesn’t work properly, it is probably the battery that is failing.
If a batteries are replaced or test as good, and the device is still not working properly, the contacts on the battery and/or battery compartment may need to be cleaned. Unseen corrosion can build up on battery contacts preventing a good connection. Using a clean pencil eraser on the contacts or just spinning the battery inside the compartment can provide a better battery connection. If you see white deposits on the compartment contacts, see What if a battery leaks?
Cleaning the front (transmitter) of a remote control and the receiver on a TV or other device can also improve performance. Dirt or grease can impede a signal from the transmitter to the receiver.
A good battery tester puts a small load on the battery by drawing a small current through the tester. Multimeters have a high input impedance and do not put a load on the battery. While measuring 1.6 V on a 1.5 V battery may indicate a good battery, measuring 1.4 V does not necessarily indicate a low battery.
Ronco Battery Tester
This is a great simple battery tester that is no longer made. Its low input impedance puts a small load on the battery for accurate results.
Gardner Bender GBT-
Recommended battery tester