some battery info you may find interesting..or not

[T77911S]

the reason i am posting this is because i had a no start problem on my jeep about 2 weeks ago and thought this may help others to understand that just because the connection does not look bad, it may still be the problem, plus we have a new toy at work and i thought i would see what the conditon of my batteries and connections really are.
so the jeep no start was due to a bad battery connection. the thing is, if you looked at the connection, there was no obvious signs of a bad connection. there was a little corrsion on the bolt itself but no large build up of corrosion around the post and terminal. if you look at the pics, the post does not really look that bad. some corrsion on the bolt but as far as the connection it looks pretty good. well, that was enough to keep it from starting.

and yes, i know those terminals are crap, but the "quick" fix sometimes remains longer than a short time it was intended, plus, i just got the jeep and they were put on by the PO.
you cant really see, but even the strands of the wire have some corrosion on them, but i will get to that later in my next post.

oh, and cleaning that terminal did fix the starting. no problems since.

[T77911S]

now onto the more interesting stuff.

the porsche started very slow the other day so i thought i would check the battery before pulling the starter, so ichecked all the cars batteries.

we got this battery tester at work a while back. it is an ALBER cellcorder, cost was about $6-7000. it checks the internal cell resistance and the intercell connection resistance, battery to battery or the resistance of the terminal connection and the cabling.

post= the post on the battery itself
terminal= the part that connects to the battery.
Rc= the internal resistance of the battery, basically the condtion of the battery.
Ric= the resistance of the terminal to post connection, and when possible, the positive and negitive cables.
u or micro ohm = 1000u ohms = .001 ohms

i did 4 tests on the batteries. first was voltage. then the internal cell resistance ( Rc) by putting the leads on the battery posts. next i checked the resistance between the post and the terminal by putting the leads on the terminals. the last test was not always the same but the intent was to measure the resistance from the post through both positive and negitive cables to either the body, engine block or alternator.

[T77911S]

as far as what is a good reading for internal cell resistance, all our specs at work say is to do a baseline on the battery new, then replace at 20% change. we have 40 batteries in one ups, all are around 8000u ohms, that is .008 ohms. we have on e bad battery that is around 26000u ohms or .026 ohms. so, for my batteries i figure once it is around 10000u ohms, it is going bad.

all readings are in micro ohms.

----------------------- JEEP BMW TRUCK VOLVO PORSCHE
voltage ------------------12-.728 .577 .663 .3 .582

Rc -------------------- 6311 5557 9271 8640 10936

Ric or terminal R. --------53 52 6339 779 172

cable R. ---------------5274 2943 10306 2007 6914


the numbers did not line up after i posted it.

as you can see i have some issues.
the jeep- high cabling resistance, remember the terminals? they were the cheap repair ones and the strands on the wire had a lot of corrosion.

the truck- the battey is starting to go bad and the resistance between the post and terminal is VERY high, also making the cable resistance high.

the volvo has a bad connection also.

the porshce- battery is going bad, the connection is not as good as the first 2 and the cabling is high like the jeep. i would expect to see it more like the BMW. the BMW and the porsche i tested the cabling the same way since both have the batteries on the opposite ends from the motor/starter. i measured from the positive post on both to the engine block. that checks the resistance of both positive and negitive connections at the battery, the cables and the connection from the body to the engine.

i went back and cleaned the terminals on the truck, again, just looking at them they did not look like they needed to be cleaned unless i took them off. when i cleaned them, the terminal resistance went from 6339u ohms to 11u ohms! the cabling resistance also dropped but not as much as it should have, so i could have a bad connection from the body to the engine. it went from 10306u to 3510u ohms.

now onto the jeep and those crappy repair terminals that clamp onto the battery cables. i cleaned the strands with a wire brush, maybe i could have gotten them cleaner, but, the resistance went from 5274u to 4285u ohms. not a big drop but still it got better.

here are pics of the truck batt. the battery was free so i had to what i could to hold it down.



looking at that you might not think it is that bad.

[T77911S]

and now for jerry's final thought.

here is web site that talks about the reduced power to the starter due to resistance.

Automobile Battery Example

i hope this helps someone that has a no start issue to realize that ALL connection and cables need to be clean no matter what they look like.

as far as what a MM will tell you, and why it is so different, i dont know. i did check some of the resistances with my MM. the clamp resistance showed .06 ohms when the cellcorder showed .00005 ohms. one of my cables was .94 ohms even though the cellcorder showed .005 ohms for ALL connections and cables. the MM is using a 9v low power battery, the cellcorder puts a 40 amp load on the battery for all the tests and it is designed to measure micro ohms.

my suggestion if you have a MM, clean all your connections, then take readings from the post to the body, the post to the engine, the positive post to the terminal on the starter, might be kinda hard on the 911 i guess, and write them down as a baseline for when something is not working.

as for my high resistance on the porsche cables? i will look into it more when i can jack the car up and get on the termianl of the starter and clean the ground strap.
the BWM has the same configuration, although it is 10 years newer, i would think both should have close to the same readings but the porsche was twice as high.

another thing to think about. if the high resistance causes slow starts, it also can put a strain on your alternator.

one good thing about the porsche and BMW, battery life is reduced by heat. putting them in the trunk helps them last longer.

[Vincent Hill]

Actually your Pic is better than seeing it in real life! I could see that the terminal was "Insulated" in the Pic and there was really no metal to Metal connection. If I ever have a battery problem in the future I may now take a Digital Picture to see what is wrong! (I just hope my camera is somewhere as good as yours is.

[T77911S]

not a fancy camera. a panasonic DMC LZ3, not expensive either.

the thing is, someone, even me, might look at the terminals and think they look ok. but when you test them with test EQ or take them them off you find out differently.

the best thing to do is clean them and put some no ox on them or something to prevent corsion, well reduce it.

[rfuerst911sc]

Some dielectric grease on the terminals and the exposed copper strands goes a long way to prevent this from happening.

[dicklague]

good information. very good information.

That tester is exotic! I have a Harbor Freight load tester and it has been so valuable in diagnosing bad batteries......and I think it costs $20.00 Great investment.......that and a good volt meter.

[T77911S]

another interesting thing. my wife had just gotten home with the jeep. the first voltage test on the jeep was about 12.3 or 4. notice the voltage went up to over 12.7 volts within about 10 - 15 minutes of shutting the car off.

a battery can actually recharge itself. if you ever see one that hasa swelled up, it has gone into a self charge conditon and over heated. so if your car battery is dying trying to start it, give it 10 minutes or so and if you can figure out what is wrong, the battery may recharge itself enough to get it started.

internal resistance is the killer of batteries. we have this hi dollar tester because we need to know that our batteries are starting to fail before they actually do, for air traffic safety.

[dicklague]

I did not mean to imply that my $20 tester is a replacement for the exotic one. Few of us have the need to afford the exotic tester.

My point was that knowing what load the battery will tolerate is important. That and a good voltmeter can tell a lot. Too many people say "can't be the battery it is only xx months old". As you point out batteries are imperfect things and in fact flaky. The more info you have the better.

Your post gives us good insight into what can go wrong and how internal resistance is a good indicator of battery life.