Here is the situation. First, I work with electricity all the time including batteries and charging systems.

Now the question. Just over three years ago I replaced the original batteries in my dually. They lasted nine year. Now the one on the driver's side is failing. I have verified equal voltage to both batteries while the engine is running, but four hours later my passenger side battery is still at 12.66 VDC on a 55 degree day, while the one on the driver's side is at 11.85 VDC. The good battery also shines on a load test, the bad battery does not.

So, these are Motorcraft batteries and I am betting Ford will not give me any allowance on the good battery as it tests virtually as a new battery.

I understand the rules about replacing both batteries at once, but I am wondering if that rule should hold in a case where one battery is still so strong. I don't have any other use for it and saying it will drag a new battery down ignores the point that it is still at the point most batteries are when they come down the assembly line. In addition, charging rates should be about equal given comparable battery condition so issues of unequal charging seem to be less applicable. I am inclined to simply replace the bad one under remaining warranty and let it ride with other.

Tell me what is wrong with this reasoning? Even if the older battery of the two only lasts another six years as the first set did, I will money ahead.

Steve

 

What does your owners manual say about batteries? if it states that they be replaced in pairs, wouldnt that presume that one battery crapping out within a warranty period would require Ford to offer you the same prorated warranty coverage on both batteries? Shouldnt matter that one still tests okay, if its stated that they be replaced as a pair? Take a close look at your manual, and see exactly how its worded.......and good luck!

 

I intend to ask and will check. Ideally they will prorate both batteries. The problem with simply going by manual recommendations is it covers a very wide range of conditions. I don't think it applies equally to all situations. The rule is a better fit when both batteries are closer to equal condition rather than one testing new and one testing as failed.

The standard concerns of the older battery dragging down the new one or charging rates being too unequal don't really apply here.

Will talk with Ford dealer where I bought them first. Maybe I will be pleasantly surprised.

Steve

 

You can replace one battery. It's "best practice" to replace both at once. But you can replace just the one in your case, and your new one may have 3 years cut off it, but like you said it's a compromise, and you will get a few more years out of your mis-matched setup.

Putting a new battery with a 1 year old battery would be a good call I believe. Putting a new battery with a 3 year old battery as in your case is borderline, but may be worth it. Putting a new battery with a 5 year old battery may not be worth the expense of the new battery. It's a judgement call there. What we try to discourage is putting a new battery with a nine year old battery like in your previous case.

 

My thinking also. I do have in print somewhere from one manufacturer that anything within 18 months is not a problem. After that I don't have any hard data.

Thanks,

Steve

 

With the price of batteries, I understand installing the one . But as stated before , a bit of a gamble . I always replace in pairs .

 

This is just an update.

Once I knew which battery had taken a crap, I was curious if I could resurrect it, so I attempted an equalizing charge twice more without success. My charger tried for a couple of hours and then signaled the battery was bad and shut itself down.

Next, although I don't normally take specific gravity measures of each cell, I did this time one cell was zip, could not even get it to read within the scale.

Called dealer and was told they would replace only bad battery and would do nothing for me on second battery that is still testing near new after three years. Just for the heck of it, I left the bad battery out of the loop and found my truck started virtually instantly on the good battery. Much better than when both were connected. I know you would expect this, but only when you are looking for it.

Off to Ford, the parts department did not even question me. Just let me drive around back, install the new one and put the old one on a dollie for them. Forty bucks including tax got me a new battery. Now it will be interesting to see how long they last as a pair.

As noted in my earlier post, the old battery still specs out as near new so it should not do much bad to the new battery until it starts to fail due to age.

Steve