I'm looking to replace my batteries.
From installing my new stereo, I realized that the batteries serve separate purposes.
After smoking my FICM the first year I had my truck from running the battery too low cranking...now I'm paranoid about sitting there with the radio on not idling.
So I was thinking of getting one "normal" battery for the starter side, and something more like a optima for the system side.
Not knowing any more than the average moron about our electrical system, I just wanted to know if that would cause any problems.

Thanks.

 

I would not use a lead acid battery and a gel battery together. They will discharge and charge at different rates and kill each other.

You could always run the stereo system off of it's own (3rd) battery and charge it through an isolator that is only closed when there is output from the charging system.

 

There aren't "two sides", the batteries are in parallel in the same circuit, and have to be to get the CCA rating up for the starter. The body electric runs off a single 4ga wire on the positive stud of the driver's side battery.

If you really need more Ah capacity, you could get a battery tray from an E-Series and stick it on your frame rail to double the number of batteries. But you'll want a big alternator to charge it all, and should probably isolate the second pair.
Hellroaring Technologies, inc., Manufacturer of Solid State Dual Battery Isolator / Combiners

 

While separating our electrical system is a good approach, instead of thinking about the storage system in two parts you should be thinking about it in starting and operating terms.

Your FICM failure from your post was a storage failure, where the storage capacity of the batteries was compromised so not enough volume was stored to maintain the voltage pressure during startup and glow plug operation. And with voltage pressure already low the volume of amps coming from the alternator was most likely not high enough to regain the voltage pressure immediately.

New or good batteries will not be depleted of capacity as much so the voltage is higher, and if using a smaller output alternator its output would be sufficient to keep the voltage in an acceptable range while the glow plugs are still on, and better still once the glow plugs turn off.

So the better way to address this is first to make sure the batteries always have enough volume capacity so the voltage does not drop below critical voltage during startup, and for this you need a starting battery.

Second you need to make sure you have an alternator that supplies the amps needed for all the electrical loads you will most likely have turned on when the vehicle is at idle. That is not a function of the batteries at all, they are for starting.

Some of us take an approach of having a high output alternator to reduce the time the FICM sees lower voltage at startup, but if your proactive about battery health you should never get into FICM issue like you had.

 

x2.

Jack is entirely on point here. Keep your batteries up and life is good. You can run additional batteries, but all need to be of the same type to prevent issues as was said.

 

Well actually my batteries dying before was a direct result of my fuel gelling over and being ignorant to it. I cranked, and cranked, and cranked. Ran the batteries down to nothing...and fried my FICM in the process. Total ******** moment. lol. That was 2 years ago now. Back then I think the batteries were still in decent shape. As little as this truck has been driven, I would almost bet that these are the original batteries. 88K miles on an 06? So I'm sure that they are just finally wearing out.


But anyhow. So I hear all points. I thought someone had told me that the computer pulled from both for starting, but beyond that they had separate purpose. Not the case. Good to know. I do plan on getting ED's upgraded alternator. But for right now, I have more pressing mandatory maintenance to contend with.

I don't sit for hours listening to the stereo. More like sitting for 5 to 10 minutes waiting on the school bell to ring when picking up the kids. I just don't want to chance running low enough to cause the FICM issues when cranking. I notice a huge difference in starting the truck if I don't plug it in at night. Temps reaching the teens at night...

But at the same token, I DON'T drive the truck a lot, so it doesn't get extended times of the alternator charging the battery. I should probably put it on the trickle charger on the weekends when it doesn't get driven at all. Would probably help.

So no on the mixed batteries. Got it. I didn't even consider the build of the batteries being gel vs L.A.

I will just get a couple new Duralast Platinum's and call it good. Then plan on getting Ed's upgrade alternator maybe this summer.


Thanks again!

 

Thanks Ed.
________________

*****, you have a better understanding about your electrical system then first implied. Your right, during the winter when we draw the highest volume of amps out of the batteries having a trickle charger is not a bad idea. Batteries will have a lower output just because they are cold, at the time when the highest draw is put on them. My recent cold morning current checks showed my truck was pulling 300a out of each battery when starting. If you have 850cca batteries that at the point of condemnation due to storage capacity it will only take 21 seconds of crank time when they are 30F to get them to the voltage where Ford sets the wrench light to warn of impending FICM damage if they are fully charged.

Driving or running time certainly can have an impact on undercharging batteries, a condition that seriously shortens battery longevity and capacity by most experts. But while having a higher output alternator can help in that regard, especially when idling, the batteries internal resistance is going to limit how much charging amps they can take. So your thoughts on putting on a charger during down periods in the winter is really good to protect your investment.

 

Quick question about the battery tender. I have mine connected to the passenger battery is that sufficient for both batteries since they are in parallel

Mark

 

Unless you have serious corrosion on a terminal it will be fine.