Do I really need to replace both batteries?
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Junior User
Joined: Feb 2007
Posts: 75
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From: Fallon Nevada
Do I really need to replace both batteries?
On my 05 the driver side battery is no longer holding a charge the passenger side does. I was always told to replace both of them at the same time do I really have to? can I just buy one now and the other one at a later date? money it tight.
Thanks
Thanks
Posting Guru
Joined: Jun 2006
Posts: 2,096
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If you just replace one, in short order it will be no better than the one its connected to.
Posting Guru
Joined: Aug 2001
Posts: 1,533
Likes: 2
If you don't replace both your just wasting you money because the old battery will kill the new battery. The old battery will draw off the new battery.
Also low voltage will kill your starter I haven't bought a starter for a 6.0 but I imagine they are not cheap.
Also low voltage will kill your starter I haven't bought a starter for a 6.0 but I imagine they are not cheap.
Lead Driver
Joined: Jan 2006
Posts: 6,267
Likes: 5
What he said ^^^^^^
some things can be left , some things need to be done. I know it can suck being tight on cash, but replacing 1 battery will just end up coming back to haunt you.
Replace both, and clean the terminals real good, and get the alt. tested. spend a few bucks, and prevent a serious failure(s).
Enjoy eating mac&cheese the next 2 weeks, its worth it.
Junior User
Joined: Apr 2008
Posts: 62
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From: In a small town.
Though I agree with all of the above, last winter Mine cranked very hard. I took both batteries out and brought them to my local CAP. They tested both batteries and under a load the driver battery dropped to 9.5 volts while my passenger dropped to 10.6 volts. Guy there said just do the one battery. I put an Exide in and its coming up on one year and no problems.. but then again its not winter yet. I did have 3 days it went town to 34 degrees already and it sounded perfect. Just my 02 cents.
Lead Driver
Joined: Jul 2004
Posts: 6,950
Likes: 510
From: Foothills, CA
Though I agree with all of the above, last winter Mine cranked very hard. I took both batteries out and brought them to my local CAP. They tested both batteries and under a load the driver battery dropped to 9.5 volts while my passenger dropped to 10.6 volts. Guy there said just do the one battery. I put an Exide in and its coming up on one year and no problems.. but then again its not winter yet. I did have 3 days it went town to 34 degrees already and it sounded perfect. Just my 02 cents.
It's pretty simple: they are tied together + to + and - to -, they will continually try to equalize, that's just the way electrons like it
-- unfortunately, batteries do not like it.my $.02
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Lead Driver
Joined: Jul 2007
Posts: 7,868
Likes: 9
From: Rhode Island
If you are short on funds, I would not replace just one battery. You will end up having to replace the old one, or even both the old and new one a lot sooner then you would have to..
While mismatching batteries can kill both, I do not think they can kill an alternator, unless ford uses some severally underrated alternator that can just barely power the truck
But yeah, say one of your batteries just died, and you replace just that one. While your other battery isn't quite dead yet, some of the cells may be failing and it may only want to be at around 11.9 volts. Now when you turn your truck off, this dying battery is going to want to try to stay at 11.9 volts, while the good battery that is at 12.6 volts is going to try to send power to the dying battery to get it to match its voltage. So during the night the good battery is going to drop below 12.6 volts, and your going to start boiling the remaining good cells in the dying battery, quickening its death. Car/Truck batteries do not like being under 12.6 volts open circuit. They deteriorate very quick below that voltage
While mismatching batteries can kill both, I do not think they can kill an alternator, unless ford uses some severally underrated alternator that can just barely power the truck
But yeah, say one of your batteries just died, and you replace just that one. While your other battery isn't quite dead yet, some of the cells may be failing and it may only want to be at around 11.9 volts. Now when you turn your truck off, this dying battery is going to want to try to stay at 11.9 volts, while the good battery that is at 12.6 volts is going to try to send power to the dying battery to get it to match its voltage. So during the night the good battery is going to drop below 12.6 volts, and your going to start boiling the remaining good cells in the dying battery, quickening its death. Car/Truck batteries do not like being under 12.6 volts open circuit. They deteriorate very quick below that voltage
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New User
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Senior User
Joined: Nov 2005
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From: Western NC Mountains
Make sure to have them load test the NEW battery before you install it. I had 2 batteries in my truck with 11/2007 stickers on them, one went bad. After they replaced just the bad one I again started having slow starts within days and believe it not the NEW battery was the low one. I took it back and they tested it and it had a bad cell. I asked them to load test the replacement AND my other one dated from 11/007, and specs were basically identical. So far everything is perfect and checking each battery separately a few weeks later and both have the same static voltage (unhooked of course).
While the advice to replace both OLD batteries at once is great advice there are always exceptions, especially if they are less than one year old.
Junior User
Joined: Apr 2008
Posts: 62
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From: In a small town.
I have confirmed this with a Ford tech. If your old battery tests fine under load then it is ok to replace just one battery. There is no possible was a battery can kill an alternator. An alternator charges the battery. If a batter has a bad cell or cells then it simply will not accept a charge in those batteries. Simple logic. An alternator can hpwever kill a battery by overcharging and causing a battery to explode. That would be the regualtor that causes this and is a whole other subject. In short yes its ok to change one battery and not have to worry about it effecting anything else.
FTE Leadership Emeritus
Joined: Aug 2007
Posts: 42,085
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From: Lakewood, Ca.
Originally Posted by Todd316
There is no possible was a battery can kill an alternator.
It's your cash, do as you wish.
