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When you cycle your packs for the 1st few times, charge them only at the listing on the batt x the # of cells. ( 3300 6 cell- .33 x 6= 1.98 or amps) In your case, .42 x 6 = 2.52 amps. no more than 3 amps. If you try to charge them like you did 3 years ago they will be dead and may go up. If you heard poping take the pack off the charger asap.