It's not a complex device - just a large 100A resistor at 12V and a simple analogue voltmeter and because it's so simple it can also be used with 6- V systems work. That's enough to give your car's battery and charging system a pass/fail rating, and it costs a lot less than the mechanic's first half hour. In my case, it helped me realize that my RV batteries were fine and I just misadjusted the switches to charge them. Great deal for me!
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