The reasons for battery voltage drop overnight
After about 60 miles driving on the highway, I used multimeter to check the battery voltage, the reading was 12.25. Then I disconnected the negative wire from the battery post. The next day I checked it agian,the voltage dropped to 10.43. My battey is only 48 months old VS. 108 month guarantee. What does cause the battery voltage suddenly drop that much?
Could be one of the cells is failing. Since you have a warranty, remove the battery and have the shop replace it for a new one. If it's a better retailer or auto part store, they will test the battery for free.
You have a parasitic draw, from something that is either shorted or drawing juice that shouldn't be using battery power. You have a multi-meter, that's good. You need to pull eacj fuse, one at a time from both underhood PDS, (Power Distribution Center) and from the fuse box behind the flip-down coin-holder, which is a real pain unless you are a midget contortionist. It's difficult to access but can be done.
https://www.youtube.com/watch?v=zdIKNnwEjIs http://www.batterystuff.com/kb/articles/charging-articles/testing-your-battery-for-parasitic-load.html http
Now, after all that, your 4 year old battery is ready for re-cycling, use the (probably pro-rated) warranty and get a new one, A lead-acid battery warranty of 108 months is 9 years.... only a selling push... no automotive battery will last 9 years except certain conditions and/or fluke, the normal life span of a battery is 4 to 6 years , maybe some will live longer. Most folks will not even have the same car after 9 years and they (the battery seller) knows it, and who saves paperwork for 9 years and can produce that paperwork warranty.... it will just be rejected anyway But use that warranty regardless. Also Now, after re-reading your question, did you re-connect the battery cable overnight or leave it off and the voltage dropped that much? If the Neg-cable was disconnected then it's simply a battery failure and as before, use the warranty, get a new one, problem solved
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