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Ripple test reading

I recently had my car battery replaced for a bad cell. The battery was less than 2 years old. The mechanic’s battery test print out includes a Ripple reading, which tested at 137mV after the battery was replaced. The mechanic then “Removed battery ground at engine side. Cleaned battery cable, nut and stud on block. Re-attached cable to engine block. Performed charging and starting system test. Test still shows the ripple to be at 130 milivolts. The alternator may have a problem in the future. Possible diodes are going bad or are bad.” So, is a Ripple reading of 137 or 130mV bad? Does it make sense what he did to try to improve the Ripple? Will I ruin another battery if I don’t do anything? Any advice would be greatly appreciated!

This is a textbook question,my favorite kind. My text indicates “Bad diodes are indicated by the presence of more than 0.5 AC volt in the output wire” So you are doing just fine in the ripple department.

Several O-scope (back to the O-Scope again,they should be used more)textbook patterns show plenty of ripple in the output but it is a nice smooth rectified output with no missing parts. Shorted or open diodes are very easy to pick out.

I don’t feel it was the ripple that did your battery in, some just go early due to poor mounting (vibration induced failures) or just substandard quality control.