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It is possible that your battery is just weak and after 5 days it is too weak to start the car - that happens with a weak battery.
Assuming the battery is fine - Parasitic electrical drain is often the result of 3rd party electronics added to OEM. Stuff like amps, security alarm, dash cam, remote start, etc.
If you are stock OEM, make sure the smart key is not stored or kept too close to the car. Try turning off the smart key switch (lower dash button) to see if that system is malfunctioning. There may have been a thread about a trunk light staying on - you can check that via the little trap door in the back seat.
My hunch is a weak battery does not go dead after 5 days. Example, when I replaced my mom's Acura battery over Thanksgiving with a Costco, I tested it. It was at 23% capacity and never gave her any trouble. I get this all the time so no biggie, just test the battery, if you have a tester, or for free at an auto parts store. This is one scenario where we can get the conclusion very fast without spending money. Another example, when I got my BMW battery replaced in 2011, I asked for the old one back, and paid the then $10 core charge. Today, that battery is 60% of it's capacity--I throw it on a tender every now and then. That's what you call spending money unnecessarily, the battery is still good today.
#dontwastemoneytestit
edit: p.s. from my experience with a failing battery, one gets caught unexpectedly. Meaning, the process would not repeat, such as, if I park 5 days, dead battery, if I drive every day, fine. But no need to speculate on a battery, it's totally different than chasing an oil leak etc. This battery is under a replace condition, yet performed fine for my mom in November, who does not drive every day. Dang that resistance is jacked, though.
Last edited by Johnhav430; Jan 17, 2020 at 05:27 AM.
It's always a good idea to start out with a fresh battery. This usually resolves most issues as well as a good starting point. Parasitic drains are not common with our cars. Try the above suggestions as well. One strong point for our LS430s is the electrical system. Good luck and let us know how you make out.
Battery Drain
Battery Dead
