Last week when it got down in the 20's truck wouldnt start cranked slow and killed the batterys so i took it had the batterys tested the one was bad so put it in was fine for a week now went to start it today same thing cranked slow didnt have enough power to start the other battery tested good last week its prob 3 years old what do u think should i replace the other that tested good??

 

When you replace batteries, you should replace both of them anyway.

 

Yes, change the other battery and check the altenator.

 

the sales guy at advance was like since the one tested good dont change them i knew i was right lol