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Explanation: A 'charging back' certainly does exist; it may be a dual-purpose unit that can either be used stand-alone to charge a battery, or to power the equipment direct from the mains when available.
Without more details, I think this is the most likely possibility.
I speak from 20 years personal experience in the electronics and video industry.
Tony M France Local time: 17:36 Native speaker of: English PRO pts in pair: 14074