Bad alternator or battery?

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2000 Toyota Echo
2013 CX-5 GS here.
My battery reads 12.3v.
Alternator (with AC/Fan turned off), reads 13.3-13.5v

The battery was completely dead after a 5 week vacation this year where it sat in the drive way.
I charged it up. The battery charger (Canadian Tire unit) told me the battery needed to be conditioned and might be bad.

I was gone for 5 days this weekend, came back and started it last night. Car started fine. Tried to start it this morning, was just under the juice required to start it. Used the battery chargers 75amp quick boost and it worked, but it gave me a low reading on the battery either way.

As I said above, I took a few readings today. The battery showed about 12.3v, the voltage with the CX5 running showed 13.3 to 13.5v. I have read it should show 14.2v.

Any clue as to what might be wrong here? Bad battery or bad alternator?


I was thinking to just pick up a new battery from Costco too.
 
:
2010 Mazda 5 Sport
Battery voltage isn't a reliable indicator. You need it load tested. Any auto parts store will do it. But yeah, sounds like a bad battery.
 

yrwei52

2016 Mazda CX-5 GT AWD w/Tech Pkg
Contributor
:
Plano, Texas, USA
Battery voltage isn't a reliable indicator. You need it load tested. Any auto parts store will do it. But yeah, sounds like a bad battery.
Yeah take the old battery to do a load test by any auto parts stores is the best way to tell whether or not the battery is good enough.

To OP, if your battery is more than 4~5 years old, dont waste your time and its time to get a new battery. Costcos Interstate Group 35 battery is a good choice with good price.
 
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CX5 GT
on mine it charges between 13.3 and 13.8. its normal nowadays the 13v range. Not like old times when charging was 14-14.2v.

probably your battery is going out or you have something consuming small amounts when the car is off for prolonged periods.