sTEm–at-Work Puzzle #45: Battery Recharge Expectations

With spring training just around the corner, we can use Yogi Berra's quote "déjà vu all over again," and return to the puzzle posted at the end of last season. You may recall that a major customer of a high performance battery manufacturer has a critical mission specific performance expectation from the lithium batteries they purchase. The quality technician for the manufacturer can only authorize shipment of all of the batteries from each manufactured lot after a statistically valid sampling and subsequent testing of all the batteries in that sample have been performed. If just one of those tested batteries does not at least meet the minimal charge/discharge specifications established by the customer, none of the batteries in that manufactured lot will be shipped to this customer. Three different charge/discharge tests are performed. A range of expected battery performance as indicated by these three tests is shown in the performance graphs below.

One battery under test had the following recovery characteristics:
  • It recovered %80 percent after it was 100% discharged and recharged 500 times
  • It recovered %75 percent after it was 50% discharged and discharge/recharged 600 times and
  • it was 30% discharged in less than 30 minutes and recovered %70 percent  after 1,200 charge/discharge cycles.

The Tech did not authorized shipment of this lot of batteries to the customer. Yes or No. Submit your answers below this blog post, or on          

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