Disclaimer: I don't have an independent method to "check" the batteries I use, but recently a friend of mine needed to change the battery in his car and I was able to check the rating of the new battery compared to what the device gave and they agreed. I use this to test whether or not I should use scattered car batteries as a backup power source and to check if the battery in my car is fine. It's very basic for the money, but very easy to give the right information. Even if you're not a mechanic, it's worth having it with you to check the condition of the battery before driving.
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