This tester seems to work fine; there are various indications of the state of charge of the battery. However, I found it difficult to understand the exact meaning of the indicator lights - some are blank, others are solid, and some are flashing - in a different order. The figures shown (a figure with 7 blocks explaining how to interpret the meaning of the various indicator lights) are really not very useful in practice - they are incomplete and poorly written in my opinion. Or maybe my expectations were just too high for such a low price.
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