Any ideas what might be causing this:
2012 RX350 has new battery
At first its fine but after a few days of no driving, it's 'dead'
Jump the car via jumper cables - works for a bit but then dead again.
Now, when I jump the car, I can drive it but the moment I turn off the car, there's like no power. As if its drained dead.

Any thoughts? This is a new battery too

 

I assume you did not have this problem with your old battery. Who installed the battery? Where did you get it? What brand is it? Is it the correct one?

Did you only make short trips since getting the new battery? It may have been installed with a weak charge from sitting on the shelf for months. I have seen this before. It may need to get a good slow charge from a battery charger to have a large enough base charge to function in your cold Canada weather. Get one of those battery chargers that can also jump-start your car, they are great to have when you need a jump and nobody else is around.

Your new battery may not have been installed properly. Make sure the cables are tight on both the battery and at the starter. Check for cable corrosion. Check they did not damage any other connections.

You need to have the place where you bought it test your new battery and your charging system to make sure both are operating properly. This only takes a few minutes.

 

Thanks. Ill give that a whirl. It's weird because its as if its drained completely

 

+1, All the symptoms of a dead cell in you new batt.

 

I agree. A new battery can be defective. That may be your problem.
Always remember that any battery can fail at any time.

 

Just a dumb question. Do you leave your keys (FOB) near the car while you are not driving it? I have heard from several Lexus owners that have left their FOB's in the car or garage that will cause the battery to drain over a day or 2.

 

Ish. I have an attached garage so its like basically near the garage entrance.

I ended up checking the battery and battery is good. Wonder if its the remote starter system draining. POS Viper car starter

 

OEM FOB's left too close to our cars will cause our batteries to drain too.

 

You checked the battery and it's good, but did you check the charging system? If not do that.

If the charging system is good, than start looking for the parasitic drain. It can be anything, for example in my old Acura the Bluetooth module was causing the battery to die over a weekend.

It may be a good idea to watch a few YT videos on finding parasitic battery drain.