2006 GS430.

Car was stored all winter, sat with dead battery for 60 days or so. Step 1: attempt jump start.

I connected jumper cables (the 100% correct way), and the following sequence happened:

1. car alarm sounded a few seconds after connecting jump cables
2. I silenced the car alarm with remote fob
3. I sat in the driver seat, and let 10-15 seconds pass
4. start button was illuminated, cabin lights on, car behaving just as normal
5. I pushed the start button
6. .... everything went blank. Lights off, no light on starter button, car completely unresponsive to everything

Any ideas where to start, based on the above?

I'd hate to throw $100 at a new battery, if the fix is well-known (though I didn't find any help by searching).

 

pull battery and have autozone or oreilys diagnose if its dead. if it is, then replace it, but 100% sure you need to replace anyways

 

Test the battery with a volt meter, if its dead take it to an auto parts store to have them charge it for a few hours. Check the terminals to see if they didnt break internally, If the parts store says the battery is bad then replace it, you could have also popped your main fusible link. Its a huge fuse under the battery that once it pops kills all electricity to your car. But start with the easy stuff first

 

Most likely the battery voltage was so low that the electronics in the car won't respond. These cars require over 12 volts to do anything and if a battery is all the way dead sometimes a boost will not help at all.

As the other have said, take it to an auto parts store and have them charge and test it.

 

Just keep playing with the start button till it start, it's a Lexus there can't be anything wrong with it

Also https://www.clublexus.com/forums/gs-3rd-gen-2006-2011/916835-2007-gs-350-won-t-start-after-battery-was-replaced.html