Battery Died Following New Sound System Installation

[zoltman1991]

Hello All!

Here's my situation for my 2020 Lexus ES350.

I had a kicker CXA400.1 wired with 8awg with an LC2i. Had this for about a year. No issues.

I upgraded the amp to the CXA1200.1 and had a local reputable shop install it swapping out for a 4awg wire.
This was done two days ago.

This morning, my car wouldn't start. It rapidly clicked and lights rapidly blinked, suggesting battery doesn't have enough juice to start.

I'm attributing this to something they did wrong.

How do I check the source problem? I have a multimeter I plan on using on the amp with the car off to see if it's drawing power. It should read 0, correct? assuming the car is off?
My guess is something went wrong when they did the work and somehow the amp is drawing power when it's not supposed to.

Please, any insight would be helpful.
I'm really hoping it's something as simple as me leaving the car on overnight, but I'm really thinking it's related to the installation.

[Euphonic]

Is the amp power light on? Is the LC2i on? Do you have the original battery in the vehicle and it’s just done?