I use a DMM to check the DC voltage (typically 12.6V quiescent before starting) because the reading is more accurate than an OTC analog needle, but OTC is close enough to to get an idea of where the tension is. The real purpose of the stress tester is AFTER the test button has been held down for ten seconds. An internal resistor charges the battery at 130 amps, which is similar to a hard cranking cycle. In this test, you can clearly see at the ten-second mark whether your battery can handle the load. Green is good! Nice to see the resistor glowing bright orange when heated! Be sure to let it cool before putting it in the box. After testing, my battery showed 12.5 volts. But it goes back to 12.6 per minute. I bought mine to test batteries for my RVs, but I've also used it a lot to test car batteries as well. Also lend it to friends who are figuring out if their battery is sulphating or just not ready for winter. My VARTA OE battery in the SUV is currently more than 7 years old, based on the current year of construction of the car (07/2012). Still treads lightly, even last winter. Everything is fine with the charging system and the battery. 90,000+ miles.
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