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These will help bypass the high frequency high voltage pulse across either the FETs or the pack terminals. Two capacitors are used in series in case one is shorted. The voltage rating should be able to withstand the pack voltage in case one of the capacitors is shorted. You want the size large enough to carry a significant current but small enough not to interfere with battery operation and to have a good frequency response. 0.1 uF is a nominal, select a different value if desired.
