memory products - Al Kossow's Bitsavers

MK48T08 (8)-10/12/15/20FIGURE 9. MK48T08 PREDICTED BATTERY STORAGE LIFE VS. TEMP.(J)a:3002001009080706050403020"" LU>-~ ~~~~"-"'- ~'" '"""~tl0/~~t 50% (AVERAGE)109876 "-5 "-'"'""'-~120 30 40 50 60 70 80 90DEGREES CELSIUSPredicting Storage LifeFigure 9 illustrates how temperature affects StorageLife of the M K48T08 battery. As long as Veeis applied or the oscillator is turned off, the life ofthe battery is controlled by temperature and is virtuallyunaffected by leakage currents drawn by theMK48T08. ..Storage Life predictions presented in Figure 9 areextrapolated from temperatu(e accelerated life-testdata collected in over 100 million device hours ofcontinuing bare cell and encapsulated cell batterytesting by SGS-THOMSON. Obviously, temperatureaccelerated testing cannot identify nontemperaturedependent failur mechanisms. However,in view of the fact that no random cell failureshave been recorded in any of SGS-THOMSON'son going battery testing since it began in 1982, webelieve the chance of such failure mechanisms surfacingis extremely small.For the purpose of the testing, a cell failure is definedas the inability af a cell stabilized a 25°C toproduce a 2.0 volt closed-circuit voltage across a250K load resistance.A Special Note: The summary presented in Figura9 represents a conservative analysis of the datapresently available. While SGS-THOMSON ismost likely in possession of the largest collectionof battery life data of this kind in the world, the resultspresented should not be considered absoluteor final; they can be expected to change as yetmore data becomes available. We believe thatfuture read point$ of life test presently under wayand improvements in the battery technology itselfwill result in a continuing improvement of thesefigures.Two end of life curves are presentedih Figure 9.They are labeled "Average" (t5001ol and (t1O/0). Theseterms relate to the probability that a given numberof failure will have accumulated by a particularpoint in time. If, for example, expected life at 70°Cis at issue, Figure indicates that a particularMK48T08 has a1 % chance of having a battery failure11 years into its life and a 50% chance of failureat the 20 year mark. Conversely, given asample of device, 1 % of them can be expected toexperience battery failure within 11 years; 50% ofthem can be expected fail within 20 years.10/13346