My 00' LX470, 379K miles, failed to start today, after making a few errands around town. It started twice, but the third time the motor turned over until battery died, but never fired. I have been finding it with a dead battery after parking for more than a day, and replaced battery last July, so I installed a quick disconnecting +terminal on the battery, until locating the source. I have a feeling the non starting, and power disconnect are related, but not sure what to do now. too far out for a mechanic. can anyone lead me to trouble shoot?

 

Do you know if your alternator is charging properly? You should get around 14v at startup, and 13-something while driving/charging. If you are charging Ok, then maybe you've got a parasitic drain on the battery?