1-A multimeter or voltmeter is usually used to test the charger's health. It is not difficult to work with and you can buy a good model of it .
2-If the battery is not used for a long time and does not recharge, this can lead to such a problem.
The right way to start is to check the charger first. If you haven't used the battery for a long time (this time may vary by type and quality and can range from four months to a year and a half or more), the battery may be damaged. Sometimes, using higher amps chargers(not voltage) than the original charger can cause a shock to the battery and return it to its normal cycle( not always).
First make sure that the charger is not damaged then check the battery.
Batteries like this are designed specifically for a device and are not conventional batteries (such as AA type) ,so should be tested with their device or with similar devices because the purpose is to charge them with their charger in the related devices.
3-In case you want to keep the battery unused for a long time you should store it with a 50 percent charge in a consistently cool area.
Lithium-based batteries should be stored in temperatures between 50 and 95 degrees Fahrenheit. You might not always be able to keep them on that temperatures, so to make things a bit simpler, room temperature is fine.