Just replaced the passenger side battery. The hydrometer specific gravity eye on the battery was constantly dark at full charge and the engine was cranking. So the plates were damaged and had to replace the battery. Group 65 battery at Cosco was only $49.99 with free 3 yr replacement then prorated to 8 years.
As you know heat damages batteries. That's why there is a blanket on the passenger side. But still it gets pretty hot.
The driver's side hydrometer eye was still green and in good shape. My X is a 2002 with the original batteries.
This got me thinking why the passenger side failed before the drivers side. My reasoning is that it was sitting in the flow of the intake until recently so it was not subjected to the unhood temps, but rather being cooled by the cold air going to the stock air cleaner housing. But now I've changed to the AIS, and that did away with the intake battery housing. It's got a blanket just like the passenger side now. But it's interesting how the Ford engineers protected the drivers side from heat putting it directly in cold air intake.

 

The 7.3L batteries are wired in parallel (this keeps the voltage at 12v). Since the passenger side battery is the first one used when starting your truck. The other one doesn't take the repeated draining and charging as bad, and thus lasts longer.

AustinS

 

Naw!
If they are connected in parallel it will draw from both. Both are needed to prevent a voltage drop and supply enough current capacity in amps. If only one battery is used or a strong one and weaker one with a weak cell, the high current load will drop the voltage and current so you get slow cranking. It takes much more current to crank over a high compression diesel engine (24:1 CR) than a gas engine (9.5:1 CR).
One battery can be used but it would have to be twice the capacity. If they did have one that big and heavy, it would probably have to be relocated to the center or it will upset the balance of the truck if place on 1 side.
Also if you do a load test to find the weak battery, you have to disconnect one, and test them separately. If you don't, both will test good, since the bad one will draw on the good one. And if you don't replace the bad one, it will cause the good one to go bad in time cycling it too hard trying to compensate for the bad one.

 

When batteries are connected in parallel, the voltage stays the same, and the amp hours are increased by whatever the two batteries add up to. In the other way to hook up batteries ( series ) the voltage would double to 24V which would be a definite problem on a 12V system. I'm sure the heat helps the pass side battery fail more quickly, but look which battery has the starter hooked up to it. No matter whether the two batteries are hooked up together or not, the one hooked to the starter first has the greatest load demand from it. That is the pass side. The more drain and charge cycles a battery goes through, the sooner it will fail.
I have my alarm, accesories, and an extra fuse block powering an inverter, stereo amps, and 8 lights that are used frequently when ignition is off wired into my driver side battery and the pass side failed first.


Austin

 

It would have to be deep cycled to cause damage. Since they are in parallel you can't deep cycle one without the other one. The heat the passenger side battery absorbs is great. It's actually hot to the touch. The driver side battery will be no hotter than ambient since it is in the cold air stock snorkel intake. Heat is a big killer of batteries, boiling off the electrolyte and exposing the plates thus damaging the cells and weakening the battery capacity and voltage.

 

Hello is right. The cables between the two are thick enough to completly equalize the drain on the batteries. There is no way that one gets a harder draw than the other. Heat is the killer.

 

If one battery failed, can the other be far behind? You might want to consider replacing the second battery. Kinda like shocks. Always replace in pairs.

 

Thanks for the info. I did replace both when the pass side went bad. I've been switching them back and forth of each other every 6 months since I replaced them in hopes they would last a little longer. I guess for the wrong reasoning, but hell, the good results should be the same.
Sorry for the mistake guys.

Austin

 

Funny, I was just contemplating the same senario when I installed my AIS this weekend. My results were the exact opposite however.

The drivers side battery was much lower on water, and the passenger side was fine. Both batteries were replaced about 1 year ago.

The only thing I can reason is that since the drivers side battery sat in the intake stream, the water in it evaporated much faster than the passenger side. I ended up adding almost a qt of distilled water to the drivers side battery.

Shrug?

 

Austin,

That's the spirit! I, too, work on my truck for extremely diminished returns sometimes. I suspect most of us do that in one way or the other, but I'll forego rotating my batteries. I have my own minutia!

Wholly Kow! Here we go again! Anybody up for a Zoodad mod for the passenger side! How about a whole new business opportunity for one our sponsor companies: An air-vented box for the right-side battery. If it was so important for the left, why not the right side, too?

Well, I'm off to look for an appropriately-sized plastic box.

Remember to call it the Pop-Mod! You heard it here first. ;-)))

Pop

 

I took the easier route and removed the blanket from the battery.

Had to go to the dictionary on minutia . Turns out I have my own minutia too.

It will probably end up being the Springermod.....or the batterypop.

 

I'll buy a round of minutia for EVERYBODY in the house! ;-)))

I need to get a life!

Pop

 

 

superarangerman2002: If it was that low on water, it could already be diminished in capacity even after you top it up. At least now with the AIS you can pop the caps easily on the drivers side. BTW now you got me worried about my new battery. I will pop the top and see if it was filled correctly from the factory.
Good thing is if you get your battery from Costco or a big chain store, they will accept full replacements within 3 years no questions asked. They had a pile of batteries that looked brand new in for exchanges.
I fully agree on replacement in pairs. I too had low water in all the cells from both sides, but the passenger side could not recover because it already had a bad cell that was irreversible. I attributed that to the heat. I'm sure the drivers side will follow soon. Something need to be said about maintenance free batteries. They need to be checked for electrolyte level if the caps can easily be removed. The ones we have on our truck are easily removed with a large screwdriver. At least the passenger side. The driver side you have to remove the terminals and take the plastic top off. After that wipe the dirt under the caps, and top it off to the bottom portion of the case right above the plates or 1 inch below the top. Use a rubber bulb to pull up the distilled water and squeeze slowly into each cell. You can also spray the terminals with battery protectant if you see white stuff on the terminals after you clean them off. And be careful of the battery acid. It can eat your clothing, paint, and put white spots on the concrete.

 

Too funny!
Cookies term "Batterypop" is spot on!