Universal battery tester
Battery testers come in various shapes and sizes but all of them are just voltage meters. Each battery type has a rated voltage. The most common ones are 1.5V and 9V batteries for our electronic devices. As the battery discharges the voltage will start to drop and that's the parameter used to determine if the battery is good or bad.
Voltage drop will work quite well, although it may be less accurate for batteries of some designs like multi-cell ones or some rechargeables where voltage may still be high but current capacity is already low.
Testers can be bought from various shops, I got this unit from Aliexpress. There are other models available there as well, they will have slightly different housing and battery connector interfaces. Either way, they should be easier to use than multimeter test leads.
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