2005 Lexus ES 330 battery has fully drained 3x since alternator change

The alternator on my 330ES 2005 Lexus (68,432mi) was replaced in 2016. My car battery has been completely drained three times now? I’ve replaced the battery twice in the last two years. I don’t want to replace it again without having some diagnostic work performed on the car. The dealer is too expensive.

Then have it diagnosed elsewhere, no need to take a 16 year old vehicle to a dealership. If there is no parasitic draw might be best to replace both the alternator and battery at the same time.

A battery from the Lexus dealer is $140 and comes with a 2 year free replacement warranty.

It is common for batteries to discharge if the vehicle is used infrequently, the battery can be recharged. To avoid having a discharged battery buy and use a battery tender.

I think the OP meant diagnostic fee is too high at a dealership.

go to autozone they will test the battery {dead cells} and alternator for free. at least you can rule them out. they can check for any codes too, that might not have set off your check engine light yet. also at night make sure there arent any lights staying on that you might not see in the day.{ glove box or under hood}