That's absolutely true Stealth, but if you test on a regular basis, like I do, you'd see that that is not the case very often. A 12V battery does not usually act like the 6V's did. They were very predictable in their decline and you could hear it in the way the starter turned over. Seldom so with the 12V, some times you can tell that the starter isn't getting all the cranking amps it should, but very often, just like Bluejay experienced, it starts great when you left to go for a gallon of milk, you come out and it goes click, and that all, or maybe nothing. I can guarantee if tested on a regular basis, in at least 90% of those, you would see a steady decline, but would not be able to tell the impending failure in the way it started.
One of the reason that 6&12v act so much different in that respect is 6V had heavy (thick) plates and therefore sloughed of over a longer period of time. The 12V has much thinner plates and being under a heavier load (more demand), when it sloughs enough off, is much more prone to develop an open circuit than the 6V.

 

FX4 Smart move to keep from getting stranded. Not very necessary I don't think, but still should keep that from happening. What I would have suggested is to invest in 1 jumper and an inexpensive load tester. Test the batteries every couple of months (takes about a minute) and you will LIKELY see the steady decline and replace it when time and testing tells you it would be wise. (I have never had a battery leave me stranded, have always been able to deal with it on my time, not the batteries time, since testing) Then, on the RARE chance (and it will be rare), that it does pull the rug out from under you, take the 1 jumper and boost the battery. I can virtually guarantee you, when tested on a regular basis, you won't be having those "surprises"

P.S. Remember, though the boosters, if not used, will hold their charge (if they have a quality battery in them) a LOT longer than a starting battery, they do need to be plugged in and charged every few months even if they're never used. I have 2 boosters and the oldest one still has the original battery in it after about 7-8 years. I do make sure it's kept charged even when not used, and it was a $200. jumper to begin with so I would expect it to last longer than the 2nd one, about a $60. jumper.

 

I ended up replacing mine today. I noticed it was getting weak a few weeks ago driving to work. The headlights were on, and when I went to hit the window switches, the dash lights dimmed a little bit. I had enough juice to get her cranked up (barely), drove it over to Advance Auto. Shes now sporting a 800 cca Optima Red Top gel. WHAT A DIFFERENCE! I never heard a 5.4 crank over sounding like a Ford Fiesta on 200 amp boost b4! lol

Oh, and for what its worth.... Other than the lights dimming when I went to roll down the window, my guages never swept back and forth UNTIL the battery failure. There was no "warning" from the instrument cluster as to something was amiss.

 

I agree.

 

If your lights dimmed with the engine running, then it's probably the alternator.

 

Chester - I'm going to respectfully disagree with you here. It can be the alternator, but it can also be internal shorts within the battery. These shorts (plates becoming electrically connected) make the battery look like a giant "sponge" or super heavy load in the charging circuit. Then, any additional load will show up in reduced voltage, causing the lights to dim.

- Jack

 

Thats what I thought also initially, until my multimeter read 14.2 volts with the engine running. Killed the motor, it then read a whopping 10.something volts. Of course, both readings were with all electrical devices off, except for that little hood light. Try as I might, I couldn't find the microswitch for it. Either way, its still so small of a draw, that it wouldn't have mattered one way or the other.

 

And, a shorted cell (not an open cell) is going to reduce the battery output to the 10 volt range. I'd say that was the problem.

- Jack