[T3] Battery Mystery

[J. Jonik]

Battery only about a year old.   Car sat for about 4 days...cold out, but not below freezing and all.  Wouldn't start today.  Horn and lights test said Battery Faded.  Last time that happened I left the radio on for a couple days...volume off.    Charged battery and all was well again.
But this time, no lights, battery or anything on.  The squeeze ball batter check thing had all the battery cells right up near the top.    Charged it for a few hours and, voila...car started.
.Is there any way to test to see if there's anything in the car that's "on"...draining the battery when the car sits for some days?   Some wire problems?
Question 2:   Can all battery cells test OK but the battery still not doing its job properly?
Then...found that the battery ground strap was very frayed...more than I noticed before...it being kind of hidden.   Replaced that with a solid battery strap...then the car started.   (I should have tried to start it AFTER re-charging, before changing the ground cable...but didn't.)  Plus, I cleaned the terminals (which weren't corroded or anything), and played with the screws at Voltage Regulator...again, before putting the battery back in.  So....is there anything to learn here?  Or is it Yet Another problem solved by magic?
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