According to bunnie, there are no ways to detect a battery bomb through visual inspection, surface analysis or X-rays. You can't spot it by measuring capacity or impedance with electromechanical impedance spectroscopy. You *could* spot it with a high-end CT scan - a half-million dollar machine that takes about 30 minutes for each scan. You *might* be able to spot it with ultrasound.
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Lithium batteries have "protection circuit modules" - a small circuit board with a chip that helps with the orderly functioning of the battery. To use one of these to detonate a PETN-equipped battery, you'd only have to make a small, board-level rewiring, which could deliver a charge via a "third wire" - the NTC temperature sensor that's standard in batteries.
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