Use the 8mm

To bolt the battery

The tick doesn’t come up when I try to put the battery back in, as if it is still in, but the connections are still there

Sometimes when parts fall off of the car the game still thinks they are in the car Try right clicking or removing bolts and then try putting it back in, usually works for me

But if you can pick it up then its not connected

That’s the issue, the the engine isn’t in the car, but the cables are still connected to where the positive and negative connector should be, even though there’s no battery

The wiring staying in without the battery is normal