▁produced ▁by ▁three ▁fuel ▁cells , ▁each ▁meas uring ▁ ▁tall ▁by ▁ ▁in ▁diameter ▁and ▁we igh ing ▁. ▁These ▁combined ▁hydro gen ▁and ▁o xygen ▁to ▁generate ▁elect rical ▁power , ▁and ▁produced ▁drink able ▁water ▁as ▁a ▁by product . ▁The ▁cells ▁were ▁fed ▁by ▁two ▁hem is pher ical - cy l ind rical ▁ ▁diameter ▁t anks , ▁each ▁holding ▁ ▁of ▁liquid ▁hydro gen , ▁and ▁two ▁spher ical ▁ ▁diameter ▁t anks , ▁each ▁holding ▁ ▁of ▁liquid ▁o xygen ▁( which ▁also ▁supplied ▁the ▁environmental ▁control ▁system ). ▁ ▁On ▁the ▁flight ▁of ▁Apol lo ▁ 1 3 , ▁the ▁E PS ▁was ▁disabled ▁by ▁an ▁explos ive ▁ru pt ure ▁of ▁one ▁o xygen ▁tank , ▁which ▁pun ct ured ▁the ▁second ▁tank ▁and ▁led ▁to ▁the ▁loss ▁of ▁all ▁o xygen . ▁After ▁the ▁accident , ▁a ▁third ▁o xygen ▁tank ▁was ▁added ▁to ▁ob vi ate ▁operation ▁below ▁ 5 0 % ▁tank ▁capacity . ▁That ▁allowed ▁the ▁elim ination ▁of ▁the ▁tank ' s ▁internal ▁stir ring - fan ▁equipment , ▁which ▁had ▁contributed ▁to ▁the ▁failure . ▁ ▁Also ▁starting ▁with ▁Apol lo ▁ 1 4 , ▁a ▁ 4 0 0 ▁Ah ▁auxili ary ▁battery ▁was ▁added ▁to ▁the ▁SM ▁for ▁emer gency ▁use . ▁Apol lo ▁ 1 3 ▁had ▁drawn ▁heavily ▁on ▁its ▁entry ▁batter ies ▁in ▁the ▁first ▁hours ▁after ▁the ▁explos ion , ▁and ▁while ▁this ▁new ▁battery ▁could ▁not ▁power ▁the ▁C M ▁for