Exactly as with testing outside the vehicle, a carbon pile test. Dual batteries in parallel may complicate testing. Generally 9.6 volts is the minimum acceptable voltage for a battery under heavy load. This as always, is temperature dependent. Usually a healthy battery won't even dip below 11 volts or so. The beauty of this testing is no special equipment is needed or driving to a parts house or removal etc.

 

I've never done testing this way, only told about it. The problem I have getting wrapped around it, and why I brought up both vehicles, is the draw of the vehicle.

The carbon pile testing the way I've done it is very specific about drawing half the battery capacity for 15 seconds. I'm including Remy's instruction which also has the temperature compensation.



So if I did the MDX for 15 seconds it's draw out of the 750cca battery is going to be pretty small in comparison to the procedure so I'm not sure the voltage drop would be the same.

On our 6.0 trucks technically we could get closer. From the starter tests I did earlier we know the starter only draws about 370-380 amps while cranking at 70°F. (Adjustment needed for that number temp dependent). So if we disconnected one negative terminal off a battery at a time we could be pretty close to the 50% rating of draw and use the fender jumper to run only the starter for 20 seconds, then check voltage. And after a cool down period for the starter, switch negative terminal connections and chech the other battery. Fifteen seconds is longer then the Ford IDS compression check, but probably not as long as people do refilling the HPOP system after rework. You could even do a wattage x seconds calculation and come up with a slightly longer time to get 1/2 CCA.

Not some I'm intending to try, but we're just theorizing here.

 

Yep, and failing battery(s) will usually choke anyway, real hard, on a test like this even if it doesn't load it up as much as a carbon pile. If results are questionable, then maybe charge thoroughly and put in on a carbon pile for a little more extensive torture. Dealers and vendors went to conductance testing because accurate load testing needs a fully charged battery to begin with, and it will need charging again after the test, and all this of course takes time. What's with the "if blue haze is seen in any cell, replace battery"? Smoke?

 

Don't forget other things for removing surface charge. Like
HEADLIGHTS. That is if you don't have LED or HID.
But you not lost yet even if you do. Try all the interior lights
along with the blow fan on high and we can't forget the seat heaters.
If you have the butt warmers turn them on.

What your after is a load. A bad battery might show good voltage with
just a meter. But put a load on it and if it still takes a nose dive. It's bad.

Don't forget the temp. Not too hot and not too cold.

Testing Battery State of Charge with a Hydrometer | All About Lead Acid Batteries

https://youtu.be/WO1F68EDZYs

https://www.batterystuff.com/kb/arti...ry-basics.html

I don't think I would ever recondition a battery. But you never know.
https://youtu.be/XuZhf2J-NIg

One other thing that he did not bring up is when charging and discharging you
can get explosive gases. So you want to work in a ventilated space and avoid
sparks and flames.


EDIT : Odd that the Youtube video window did not show up. Oh well.

 

Headlights will remove the "surface charge", but it's not any kind of a load test. The usual routine is 5 minutes (engine OFF) on high beams, then wait a minimum of ten minutes and measure voltage at posts. It will "bounce back" in that time to an accurate state of charge reading. 12.6 volts for flooded conventional batts, 12.8 for maintenance free sealed batts.

 

I didn't get the blue haze either. I've never seen it. But I'm just more comfortable with a more controlled test. The time savings of not doing the charging before the carbon pile or spec grav was an enlightening during my first use of the electronic tester.

 

I bought an entry level Midtronics conductance tester, just because I like gadgets sometimes. It works well to keep an eye on battery health over time, too. It would be real useful if one had a pile of batts to go over for some kind of triage or whatever, or maybe even when buying a new one.

Also useful for testing a disabled vehicle battery before providing someone a jump start. If the battery is defective, especially, it's not worth the risk.

Think I read here, someone who worked for a summer at a battery manufacturer. They measured the voltage of the batts coming off the line. The ones reading the highest were the more expensive batteries, with longer warranties. There is no internal difference between a 72 month battery and a 36 month battery other than the sticker on the case, and of course the price. They are simply betting you won't need to make use of the warranty.

 

My routine for probably the last decade was to bring a voltmeter with me and get the highest voltage batts at the store. I've usually found some differences even with the same month stock.

This last pair for my 6.0 I forgot the Fluke and just grabbed two. A mistake I realized when I got them home, and has dogged me since installing them. I don't see the balance out of the batteries now when I've checked the amps out of each, despite the upgraded cables. I switch the batteries and the output goes with the battery.

I took the capacitace tester with me the last batt and grabbed the highest CCA. Well how this goes, but the cap tester may be the tool I'll take in the future. After all, it does show volts, too.

 

The cheapie I bought can't determine CCA, it has to be inputted manually, then it determines if the battery is Good/Bad. They can sort of diagnose bad cables and connections, on the principle that they are normally connected directly to the battery posts for the most accurate test. By connecting to the engine block for example it would show a failure if there was excessive resistance.

 

Ahh, once again Tedster has posted, until I look for the post. Let's see if after I post this his post shows up.

Edit, yep it did.

 

Playing around I have found that I get a different measurement trying to go through the terminal clamps. Much better to go direct to posts. So 0.0002 ohms per clamp does influence the readings.