yesterday morning-6 am- 45 degrees-New Orleans suburb I'm in a hurry-substitute teaching-long term assignment-and I had to give 2 tests Turn key- click click click- Yeah it had been cranking a bit slower the day or two before but it starts soooo quickly-I never worry about it What battery do I need It has a May 2009 Energizer- 4.5 years old- E78-S is on it-sideposts(I hate side posts) so are those Optima red top yellow top "worth it" Oh it starter yesterday evening-and this morning- 20 degrees warmer-barely cranked but this old suburban starts soooo well-just a hint of cranking is all it needs-most reliable used car I have ever had. So any chance it is the alternator?Forget how to tell alternator from battery failure -other than my usual-Buy second battery-it dies-means it was the alternator.Usually complete alternator failure car won't "run" after the battery is drained-knew this girl-her MGB alternator would croak regularly-1970's-I would bring her a battery-get that Brit POS home(fun car other than Prince of Darkness electrics-and it was too slow) Guess I should hook up the voltage tester? What would I look for. Suspect it is the battery-lazy. 4.5 years on battery-is that about it for a Energizer? Oh half turning the key-Voltage READS 10 volts- ONCE RUNNING 14 VOLTS Thanks Charlie PS Heck- THE 2006 prius battery lasted 7.5 years-and it might still be working if someone hadn't left an interior light on- this POS Energizer- 4.5 years 3 year full warranty 8 year prorated-Sams- USUALLY prorated warranties mean you have to buy the same POS battery again How "good" are those Optima batteries? Worth roughly double the $$?