The symptoms of this are the same as when my battery terminal broke off. The cables are so short and heavy that they had to be eased out to allow the battery out. It had only been out a couple of times and the angled bracket work hardened and broke where the cable joins it. Whilst the bracket is massive (as battery terminals go), the bit that joins to the cable is not and is a weak point. The symptom then was that everything went off, because all power was lost. It had been playing up before that with the battery seemingly not holding charge, and I suspect when the joint starts to work harden and crack it geenerates heat when you use the starter which makes it worse.
I replaced the earth (lower) cable with one from Halfords that was a few cm longer. That enabled me to re-route it so it wasn't so tight.
Of course ... might nto be anything to do with that.
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