Battery keeps dying.

My battery has died a few times in the last 2 months. First time it happened was after leaving the obd2 reader in for2 weeks and I believe it was the cause. The second time was after doing some modifications where things were tested leaving the keys in the ignition a few times. This 3rd time the car door was left not quite shut overnight and not activating the door sensor thingy. All of this has also happened since I disconnected the instrument panel to add the chrome rings. Could I have somehow reconnected it in a way that is draining the battery or is that not possible?



Each time looks like a clear cause, but should the battery have survived a bit better or am I just not giving it much of a chance.

No idea how old the battery is.

I'm thinking I just need to replace the battery, but is there a way I can be sure it is the battery and not the alternator or something draining it?



If I need a new battery which one do I need? Never had to buy one before and halfrauds (convenient) has a few different ones.

Thanks.

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