Electrical issue/starting

[GypsyOwl73]

Hello everyone,
I’m new to the Land Rover family and have been doing a lot of research on an issue I’m having, but I’ve hit a bit of a wall and wanted to reach out here.
I have a 2016 LR4 that had been sitting in a garage for about 4 years. When I first got into it, I checked over the wiring, belts, fuses, and connections, and everything looked good. I expected the battery (and key fob) to be dead, so I replaced the battery. After that, it started right up. I let it run for a while, pulled it out of the garage for the first time in years, then parked it back inside and shut it off.
The next day, I came back, cleaned it up, added windshield washer fluid, and tried to start it again—but it was completely dead. No power at all.
At first, I thought maybe leaving it at full ride height drained the battery (I read that somewhere), so I rechecked the battery connections and even exchanged the battery just in case it was faulty.
Today I did more digging and started reading about the high-amperage “mega fuses” (300A/400A). I also found a loose wire near the battery that I’m not sure where it’s supposed to connect—I’ll include a photo in this post.
For reference, I haven’t checked the passenger-side fuse box yet.
If anyone has any ideas or suggestions, I’d really appreciate the help. Thanks in advance!

 

[jlglr4]

Assume from your post that the megafuse checks out. When you say no power at all, do you mean no power to the starter or no power to the whole car, i.e, if you turn on the ignition (without pressing the brake), you get dash lights etc or just nothing?

 

[powershift]

Use a volt meter and check power at the battery, fusebox, etc.

 

[BBLR3]

I also found a loose wire near the battery that I’m not sure where it’s supposed to connect—I’ll include a photo in this post.

That wire doesnt connect to anything. Was something that was used before delivery I think. We all have it.

 

[txfromwi]

That wire you are showing is used only in initial shipping from the factory. It connects to a battery disconnect relay that is installed at the factory and removed at the dealers. Make sure that cap is secure, it can sometimes come off.

There is a pyrotechnic coupling at the battery that disconnects the battery but the only way to make that fire is to deploy the airbags.
I have never heard of that activating all by itself.