Several issues associated with the battery drain. If you have any after market device installed, your first step is to disconnect them, one by one, then hook up an Amp meter to see any improvement. Intermittently problem is hard to diagnose. I would try with a brand new battery.

 

Thanks for the reply , Its randomly happened 3 times since a new battery installed 3 mo ago
I will try just locking the door at night and not activating alarm, as someone suggested ...

 

Quite often it is the light in the trunk. Even though the lid is down, the light is on. You can try taking the bulbs out temporarily and see if that resolves the problem.

It could be the voltage regulator on your alternator is going bad and it isn't charging on a consistent basis (Which is why you needed a new battery) If you go to an Autoparts store, they can check your battery and alternator. If you go to Autozone or Oreilley's it is free for them to check those two things

 

Added a battery maintainer. Easy plug in

 

Thanks for all suggestions, I may try plugging in a trickle charger. Is there any chance that not turning on the stock alarm on the fob could make a difference?
I changed trunk light bulbs to led bulbs last year , but could just remove them as not necessary......
Doubt its an alternator issue, as we only drive short trips around our home..
Since its intermittant ,and rarely happening , I don't dare take it in to have someone start an expensive search and just replace random parts,
Other than this , My sc430 is a dream ,had it many years, and by far the best car I have ever owned

 

If you don’t drive your car often like most of us here, the best and easiest solution for your issue is a battery tender. Some member installed the connector plug near the windshield wiper for ease of plug and unplug. The instruction is in one of the battery drain threads. Search for it.

 

Battery tenders are a must for cars not used as daily drivers, most especially during this Covid times. Easy connect features on most recent style tenders with intelligent battery chargers.

 

Here you go https://www.clublexus.com/forums/sc4...y-charger.html

 

If you go to Autozone or Oreilley's it is free for them to check

 

If your trunk lights are LEDs, they are not the culprits.

 

After my 5-year-old Interstate AGM bit the dust due to lack of driving during Covid, I replaced it with a $300 Optima yellow-top and invested in a $200 Optima charger. My old battery only had issues if I didn't drive the SC for three weeks, until it crapped-out entirely. I plan to keep this new battery on the charger when not driving for weeks. The Optima charger analyzes the battery each time it is connected and then alternates and modulates the voltage and amperage among charging/conditioning/maintenance modes in order to help prevent the damage incurred when a battery sits in a depleted state.

I'm not sure if the Optima batteries and chargers are worth the extra money, but I will find out when I see how long this one lasts.

 

Mine is a daily driver, but over the weekend, it HAS suffered a few episodes of a light being on all weekend due to our being too gentle with the doors. After a severe drain event like that, the battery is never the same again. So, I end up replacing the battery. After two such events, it became evident that daily connection to a batter tender was way better than

1. Ruining a battery and needing to buy a new one
2. Turning the key while trying to get to work only to hear just a "click"

With the connection point placed so conveniently on my car cars, it's really no effort to connect and disconnect EVERY TIME. Add to that the benefits of the tender doing its conditioning work daily and seeing the battery condition as indicated by the CTEK's status lights each morning.

They are not free, but still preferable to paying for batteries on an accelerated schedule.