HP - I'm a little confused by your use of the term 'dip' for both the AC event and the DC response. Is it the case you experienced an outright outage on the AC for 50 cycles, which then produced a 52V sag on the DC for a 10 cycle duration?
On the face of it, I'd guess that the magnitude of the DC sag (52V) is of greater concern than the duration (10 cycles). I think I'd arrange a test discharge to determine current battery capacity.
Radar
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