This has been a recent issue. I start the car, the voltage jumps to 14 then slowly goes back down to 12 volts. Get this though, when I turn my headlights on, it jumps back to 14.2! I don't know if anyone has had a similar issue.
No, I haven't cleaned the ground yet. Thats my first guess.

 

I'm sorry but I don't understand your problem. Does your car not start? Does it not run?
Depending on the battery condition the voltage is normally around 12 volts. When you start the car the alternator kicks in and supplies power to the battery to replace the power lost from the battery when starting. This briefly causes the voltage to surge to 14 volts before settling back down again. When you turn on the lights there is a sudden draw from the battery again which the alternator senses and supplies power to the battery to help out. The voltage may stay around 14 volts as long as the lights stay on. This all sounds perfectly normal to me and I don't understand why you think there is a problem.

 

The car starts and runs fine. I have the volt meter that plugs into the 9v outlet. For a long time the voltage has been 12 before start, then consistently 14 while running. AC or defrost will knock it down to 13.5 or so. Nothing crazy. I realize that is normal.

Lately, when I start the car, voltage climbs to 14 then settles at 12 while running, no AC, defrost, or phone charging. While the car is running, if I am charging a phone and got AC on, voltage goes to 11.5, which seems like an issue. The only times I've noticed it jump back to 14 (while running) is when I let off the gas and coast, and when I turn on the headlights. It hasn't been acting this way until recently. I don't know if it's a problem per say, just that its out of the norm.

 

I have an Ultraguage and can confirm that when running/driving the voltage of my 2010 Fit Sport bounces around from (approximately; I'm not staring at it constantly) 13.7 to 14.3.

I would think that if you're seeing 12v while the car is running that is an indication that the alternator is not charging or is oscillating between charging and not charging. Probably a good idea to check the grounds.

 

A fully charged "resting" car battery should read 12.8V. A fully drained battery under no load should be no lower than 10.8V. High electrical loads (such as starting the engine) can momentarily pull the voltage in to the 9V range but it indicates the battery is either mostly drained or failing. Various vehicle electronics such as the radio will typically mis-behave and/or shut down somewhere in the 10V range.
13.6V is "float" charging - the battery can be charged to full and held at 13.6V without any adverse effects. The battery will hold what's known as a "surface charge" immediately after being removed from a charger: It will continue to show an elevated voltage until a load is applied, then quickly drop to the expected "resting" voltage. 14.4V ("fast" charging) charges the battery faster but can produce hydrogen gas, overheat and reduce the longevity of the battery if left in this state. A proper charging system should reduce the voltage to 13.6 or lower once the battery reaches full charge. Voltages over 14.4V generally indicate a bad voltage regulator (part of the alternator) or bad test equipment (volt meter).

 

These vehicles have ELD. Depending on electrical load, battery temp, battery amp draw etc., for gas saving purposes it disengages field activation of the alternator. No load on alternator = less EM resistance/better gas savings. When coasting it also activated as an "engine brake" to utilize charging more efficiently very similar to a Prius.

Below 12 v is a sign of a battery issue when resting. Advise to check IR and replace accordingly. If IR is above 10? mOhm? (Double check value) Then replace. But the below 12 resting is it's own indicator. Use a 51R, not 151. Cheers.

 

I recently had this issue after I had my mechanic install a new serpentine belt. My voltage is usually at 14V but it was dropping to 12.5 occasionally. I. Hoping it’s not my alternator that’s starting to go and just issues with the new belt and the tensioner (not new) finding their comfy spot.

 

Sort of. Below 12V but above 10.8 can simply mean the battery is in the lower half (50% or less) of its state-of-charge. Unlike the lithium battery in your phone or traction batteries in hybrids and EVs, lead-acid batteries (which include most 12V car batteries) don't do well when frequently "deep-cycled". Meaning you should avoid using that bottom half of the battery's capacity as it shortens the service life of the battery. By the way, it's not a hard cut-off "< 50% = bad"... The less of the battery's capacity you use and the more it stays at 100% charge, the longer it will last.

For those not familiar, this is "Internal Resistance" which would be written R-[subscript]-internal by science and engineering types. It describes how much the battery's voltage drops for a given electrical load (amps, current). More IR = more voltage drop. IR increases slowly over a battery's service life, ramping up at the very end. A battery with high IR may show a fully-charged voltage at the terminals, but the voltage drops rapidly to the mid-single-digits when the starter is used. That drop in voltage results in the starter not getting enough power to turn the engine's crankshaft (electrical power is measured in watts (W), which = volts * amps... you need both to do work). Or the crankshaft may turn slowly, but while doing so there's not enough battery voltage to run the ECU, ignition, fuel system and such, so the engine doesn't start.

 

I have had a suspicion for a while that Honda was 'cooking the books' when they went for some of the numbers this car produces for MPG. I have best those numbers, but it's also hard for very normal driving to meet those numbers. I have only disconnected my battery maybe 4 times in almost 7 years. Each time I disconnect long enough the ECM may reset certain factors. The result is something that I don't understand why, if intentional, that Honda would do on purpose.

My experience lasts maybe 500-1000 miles, so maybe it's time based and not distance based:

• Most acceleration will drop the charge to what I estimate to be the current battery level of 12.7 ish...
• Deceleration will immediately kick to 14.x volts.

It seems super intelligent and programmed into the logic of the car, but it stops each time.

How often do you disconnect your battery? I know back when I messed with cars all the time, it was probably rare for me to go a 1000 miles without messing with the battery.

 

Just curious what your experiences are regarding fuel efficiency in your Fit that leads you to these conclusions?

I keep a spreadsheet of my fuel efficiency for every tank, and also write down the reading that the car provides. I have had many tanks where the difference between the two is <0.5 mpg and it's rare for the discrepancy to be more than 2-3 mpg. There is no pattern that I can discern as to whether the pump or car fuel efficiency will be higher, which doesn't lead me to support the idea that "Honda is cooking the books."

My lifetime average in my 2010 Sport A/T, over 25K miles of ownership (basically from 100K to 125K miles), is 38.4 mpg. On pure highway trips I get 40-44 mpg. I don't really do anything special except that I don't speed, I don't do jackrabbit starts, and I look ahead to plan my throttle and brake inputs (i.e., roll to stop signs and lights instead of emergency braking at the last moment). Just the basics of getting good fuel efficiency in any vehicle.