How should I change the battery on a modern car?

Can you please provide me with appropriate advice and guidance on what precautions are advised and methodology applied when replacing the battery on modern cars with sophisticated electronics, such as a BMW 3-Series or Citroen C3?
It's best to somehow maintain a permanent current, but there is an HonestJohn video about this on our YouTube channel here: youtu.be/P7L074W5YfY
Answered by Honest John on

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