Battery Charge?

[Kimberly G.]

Last night I stumbled upon the information about the “Engineering Test Mode” and am geeking out. Tried it on mine this morning and it worked like a charm and gave me some interesting information about my battery.

after driving for about 5-10 minutes, the display showed 11.7 volts, and after driving for another 40-50 minutes, charge showed to be 12.1 volts. This was without the engine running.

Outside temp was ~35F.

Am I correct to interpret this to mean it’s time to replace the battery? It’s about 2.5-3y old fwiw; it’s a Motorcraft IIRC.

 

[peterk9]

Welcome to the Forum Kimberly.
I'm not familiar with that test mode, but to me, it seems the battery is good.

Peter

 

[Kimberly G.]

You may be right! It shows 14.2 volts with the engine running. (Seems to be ideal from what I’ve found all around!)

 

[Odrapnew]

I'd argue your battery is running low.
If your resting voltage is only 11.7-12.1V, it's quite low.

Running voltage of 14.2V indicates your alternator is working.

I'd have your battery charged and load tested.

From Haynes manual.

As we've discussed the resting voltage should ideally be no lower than 12.6V. Bear in mind that when a battery goes down to 12.2V it's actually only 50% charged, and below 12V it's classed as discharged!

 

[Barry Trobaugh]

If I remember correctly, a fully charged battery will reade 12.7v

 

[Kimberly G.]

The plot thickens. Battery test this afternoon showed resting voltage at 12.5, but driving home in the engineering test mode it showed 12.9 most of the way! (Bearing in mind it hung at 14.1 last night, and earlier today, load same)

How accurate is that measure from the ET Mode??

 

[stuarto]

You may be right! It shows 14.2 volts with the engine running. (Seems to be ideal from what I’ve found all around!)

Confirmed, should definitely be 14.2 volts with engine running.

What voltage is the test mode actually monitoring? Is it definitely the battery? Also, where is it measuring it?

 

[Kimberly G.]

Confirmed, should definitely be 14.2 volts with engine running.

What voltage is the test mode actually monitoring? Is it definitely the battery? Also, where is it measuring it?

See that’s what I don’t know. I definitely need to do some more digging.

 

[stuarto]

See that’s what I don’t know. I definitely need to do some more digging.

You have a voltmeter?
Also, is the car starting ok? Not slow to turnover?

 

[Kimberly G.]

You have a voltmeter?
Also, is the car starting ok? Not slow to turnover?

No volt meter (had it tested at a store), car starts ok for the most part- I swear it sounds slower first thing in the AM.

 

[tlveik]

Confirmed, should definitely be 14.2 volts with engine running.

Non necessarily. Mine dials back the charging voltage to around 13V when it knows that the battery has been fully charged. I don't know what year they started doing this smarter charging.

Tom

 

[Kimberly G.]

Interesting to know! Car was running ~13.1 last night on the way home but has held a strong ~14.1 running today. Still starting around ~11.8 here and there (first thing in the morning, after 45 mins sitting at Costco).

just trying to figure out if I am reading too much into this or is my battery really slipping.

 

[JAPeterson]

I would say that if you are not using a actual volt meter connected to the battery you are reading too much into it.

Reading it through a monitor and the ECM I believe that you can get variations in the voltage readings. Before I would start to worry I would get the actual readings by using a digital meter connected directly to the battery

 

[J_C]

It uses a charging strategy that is supposed to eek out slightly higher fuel economy by not always using the alternator to charge 100% of the time, instead of the old school, always charging while running strategy, so you can't necessarily go by the voltage.

It also monitors the battery voltage and compares to the charging strategy and when it detects the battery is not holding as much charge as it should, will display a message "system off to save battery. Turn key off or start ignition" which, unless it has been several days since you drove it (in which case you might try just putting it on a battery charger) means you should get a new battery soon - but it should still start and run at this point.

I would wait and not get a new battery yet unless you find it is cranking slow to start, unless failure to start would be a severe hardship then I'd go ahead and replace it.

 

[Steve18Sport]

I have an Aeroforce Interceptor gauge connected to my OBDII port which reads battery voltage, so here's my experience with it. Typical charging voltage is 13.7-13.9 with the engine running, unless the battery is fully charged in which case it often drops back to 13.3-13.5V. With the engine off, there is quite a bit of voltage drop when accessories are on or even just the door is open and the screens/lights are on...in the range of 0.5 V. So a fully charged battery might appear to read only 12.1 or 12.2 V because of the current draw. When I've previously tested the voltage readings against a digital voltmeter directly connected to the terminals they have matched up well.

There's really no way to be sure about your battery based on voltage, you would need to use a battery tester that measures internal resistance. You can find them fairly inexpensively and it's a good tool to have for making good on battery warranties. Another option is to keep a lithium jump starter with you as a backup.