Electrical Lifepo4 Battery Replacement

I'll post my solution.

Solution:

To back up the voltage regulator on a standard alternator, an in-line regulator at 14 volts can be used. These are a little expensive ($150) and will cause a drop out of about a volt. If the car charges at 20v, it will drop to 14v, if the car charges at 15v, it will meet the desired 14v charge. However, this would also mean a car charging at the ideal 14.4 volts drops to 13.4 volts. That's perfect for a LiFePO4 battery, because that is where they last the longest. It isn't ideal for a lead acid, which should be charged at 13.8-14.2 v (14.4v Max). 13.4v is still going to charge the battery and keep systems in the car functioning properly, but won't recharge a drained lead acid battery up to 12.8v very quickly.

If a car manufacturer or enthusiast wants to have a perfect system, they should use a LiFePo4 battery with a good voltage regulator at 14.6 volts, with an in-line regulator at 14v output, to ensure a voltage no higher than 14v and a much more stable charge. For a lead acid battery, an alternator with a 14.8v regulator backed up by a 14.4v in line regulator would be ideal. Standard charge would be at 13.8v and never more than 14.4v.

I'll keep looking for a cheaper solution, but that seems like the best option, expensive as it may be.

It looks like manufacturers are stating a safe overcharge of up to 4.2 Volts per cell without damage to the battery, so the LiFePO4 can handle 16.8 volts. A lead acid would boil over or explode by then.
http://www.powerstream.com/LLLF.htm

I'm going to run the LiFePO4 battery with only a fuse since that's higher than a lead acid battery could handle.

I'll post updates on the battery's performance throughout the winter and in the spring when I put my Mustang back on the road.

"I'm going to run the LiFePO4 battery with only a fuse since that's higher than a lead acid battery could handle."

They have the best track record of any battery chemistry in motorcycles, electric cars, electric motorcycles, solar power, wind power, RC cars, etc. Mustangs are not different from other cars when it comes to electrical needs, and only slightly different from modern motorcycles. I have been aware of its potential for about a decade, but the cost has always been too high to get adequate cranking amps until more recently.

People spend a lot of money on a fiberglass hood or aluminum heads to save weight, 100 dollars more than a lead battery seems minimal by comparison.

I don't have the link from the specific one, but google something like this.
http://www.chargingchargers.com/converters/sdc60.html

The stock regulator should put out 13.8 to 14.2 volts and a maximum of 14.4 volts. This, as well as the 14.8 volts my worn out regulator peaked at should work just fine. In fact, my lead acid battery was probably at more risk of over-voltage than the new lithium one.

It will only lose 1 volt, which is 13.8, which is acceptable.
There are plenty of dc to dc converters that handle more than that.
You don't need to put it under the hood.
This is an idea for enthusiasts and potentially car manufacturers, as there are other benefits to stabilized voltage. Not for me.

Thinking a LiFePO4 Battery is less safe than lead acid is a miss. Though that's chemistry, so it isn't a lack of electronics education or experience.

The Mustang electronics system was never designed properly, a 65 Watt alternator? There's a reason people upgrade to 95W or 3G alternators. This is the same thing, an obvious upgrade to those who know batteries. I built an electric vehicle, among other things, I know batteries. I'm more surprised we see lead acid in cars still, I wonder how high gas prices have to go before they swap them.

Typical internet communications. Debating irrelevant points and not comprehending the message. The battery works. I just want to make the system better and share it.

@stykthyn What in our conversation has led you to believe that the battery is not better suited for the task than a lead one? If you want to move your CG, you can add weight lower than 2-3 feet off the ground and farther back than the trunk/hatch area, meaning less weight to accomplish the same task. You also won't have the possibility of venting fumes in the car.

A lead acid battery would explode at the voltage it takes to damage a LiFePO4 battery.