marathiboy Posted December 13, 2023 Share Posted December 13, 2023 I have 2002 es300, with 130k, and 9 year old optima battery. Car us running fine, starts at almost first start even in below 32 f weather. Due to battery age just wanted to check and local shop and they tested under 2000 rpm and told me alternator is bad replace asap. So I tested again with my cheapo meter Engine off battery 11.85v Engine turned on it dips to 9.9v but comes right back to 13.8v and stays there. Climate is set to auto, there is dash cam, but no other load like radio etc What voltages I should be seeing? Is alternator really going bad? Appreciate response. M Quote Link to comment Share on other sites More sharing options...
RX400h Posted December 14, 2023 Share Posted December 14, 2023 Quote The running voltage of a 2002 Lexus ES300, when the engine is running, should be between 13.5 and 14.8 volts1. This can be measured at the battery terminals. If you switch on the accessories in your car, for example, headlights, AC fan at full speed, and interior lights, the voltage should remain around 14 volts. If it drops and remains below 13.5 volts, it indicates a problem with the current supply from the alternator1. Quote Link to comment Share on other sites More sharing options...
unknwn Posted December 15, 2023 Share Posted December 15, 2023 Your battery needs to be -fully- charged, and only then can you depend on a diagnostic voltage reading. A battery at rest, with no draw, and after an adequate charge cycle -should- read 13.5 volts. A charging system, functioning normally, on an adequately charged battery -should- provide a reading of 14.5 volts at several thousand RPM. A Battery load test (using a carbon pile tester) will only provide a testing result of 'good' , on a battery that has received an adequate charging cycle. That aforementioned charging cycle -can- take many hours depending on how flat/discharged the battery, it's make-up, and the ultimate charging rate (slow is always better, the battery doesn't so easily suffer over heating). Quote Link to comment Share on other sites More sharing options...
carlexes330 Posted February 3 Share Posted February 3 Wow a nine year old battery and its been a battery too long hence your low 9.8 volts . The alternator is definitely bad. Replace with a new not reconditioned one. More expensive but worth the cost unless you want to be replacing it again. Charge your battery and then get it tested at one of the pep boys, kragen autoparts stores. If it checks out good then no need to replace but usually batteries last 4 to 5 years so now you battery voltage is 9.8 v you may finds its trash even after recharging as the capacity is diminshed. You alternator is dead and unable to charge your battery , Good luck and post your update Quote Link to comment Share on other sites More sharing options...
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