I'm having what I can only describe as an intermittant charging issue.

for the last few days I'v had to boost my car three times.

yet, when the battery is fully charged, it'll take 2 10 second full load tests without discharging significantly. yet *sometimes* when I start, the glow plug cycle eats most of the CA's
I've tested the alternator and it is functioning, hwever it's putting 12 or less volts at idle as opposed to the usual 14.55 I see on other systems.
when I increase the engine speed the volts measured at the battery are 14.55 and up...

bad regulator? bad brushes? bad tests?

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RIP: 80 300SD
RIP: 79 450SEL
2002 E430 4matic (212,000km)
2002 ML500 'sport'

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FACEBOOK: PANZER450

Have you checked the cells in your battery? Maybe low on distilled water?

Based on your description, I would be suspect of your battery.

Have you checked the draw on the battery when the car is off? Maybe a circuit is drawing amperage when it should be off (trunk light?)

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83 300d - 390k

Pull the battery and have it load tested.

If it passes the load test, then you've got a cabling problem. Remove the ground strap from the engine and the body and clean the mounting points. Reinstall.

Remove and clean both cables at the battery. Use the tool that shaves some lead off the inside of the clamps.

Remove the negative cable from the body and clean beneath it.

The alternator is fine.

1984 300d Turbo 140,000
Removethe Ground Strap Under The Engine To The Transmission
Clean And Reinstall

Thanks, Brian!

Well, then I'm 99.9% sure it's my battery then, because my ground cable is 1ga that goes from the chassis right to the engine, and there's a go-thru battery terminal in the middle, all is clean because it's all new. I load tested the battery twice with a resistance type load tester and like I said, it took two load tests without discharging.....which makes me thing alternator, but then you say it's fine...it's supposed to run less than 13 volts running?

I did set my idle speed down a tad last week just before this all started...my tach doesn't work so I have no cle what RPM it's Idling at, but could it be too slow that the alternator is operating at an insufficient capacity?

I will buy a new battery! 100Ah os better than 88? can someone explain Ah spec for me please? I may be skilled, but I'm a retard when it comes to charging systems....

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RIP: 80 300SD
RIP: 79 450SEL
2002 E430 4matic (212,000km)
2002 ML500 'sport'

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FACEBOOK: PANZER450

Hows your voltage regulator?

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91 350SD
14 F150 Eco
19 Fusion Hybrid
11 GT500

A 100 Ampere-hour battery will deliver 100 Amperes for an hour, or one Ampere for 100 hours, or any other combination that multiplies to 100. The catch is that this rating (the 100 Amp-hour or whatever the number is) is really good only at what they call (in the fine print) "at a 20-hour rate." Meaning in the case of our example, the battery is supposed to be able to produce 5 Amps for 20 hours before the voltage falls too low (I forget what "too low" is).

So more is better. The CCA (cold cranking amps) is supposed to rate how well a battery can produce a large current (for the starter motor) for some fixed period of time (a standardized number like 30 seconds or a minute) when it is cold. Again, a bigger number should mean a better battery. Batteries with more CCA generally have heavier plates, internal connections, and outside terminals.

The Amp-hour rating has been a standardized method of rating batteries for many years. It is still used today for car batteries but has more meaning for small batteries powering flashlights and electronics (generally rated in milliamp-hours) and large batteries for electric cars and other uses requiring a fair amount of current for as long as possible.

The CCA rating is a newer rating and is better for IC-engine car batteries, because they require enormous amounts of current to spin the starter motor. Thus, all other things being equal, you should choose the highest CCA rating that will fit in the battery compartment and in your budget.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

There is nothiing like buying things you do not need. Further testing is indicated here. I would make up a cigarette lighter end feed for my voltmeter and see what that alternator is putting out over the period of a day or twos use. My guess is it may be falling down. Just use the volts function to make sure it is staying up to about 13.5 or greater when driving around. There is already some indication of a charge problem as you say you get no apparent charge indication at idle with your meter. You will also or should go over any and all connections in the charge circuit before absolutly condeming the alternator. Especially the grounds even if they look good. You are aware you can check the grounds by voltage with engine at idle looking for a voltage drop? Or just run a booster cable from the negative terminal to a clean cinnection on the alternator case and remeasure your idle voltage. It should be higher than when engine is off. Make sure you all electical loads are turned off before test even the sterio. Yes of course it could still be the battery but you will have more information to go by before spending money. Just monitor the system under use. Or I should say thats how I would proceed if my battery passed the load test and I had no indication of charge at idle with no electrical load at that time. If the red charge light is on, very dim, or flickering at idle especially forget the battery for awhile.

Conductance Load Testers are nice ( it tink dat is wat ur talkin aboot) but they shouldn't discharge your battery more that .01-.02 vdc anyway. Test your battery when it is hot (100F but not hotter than 120f) and when it is cold like 32f , many batteries with crappy electrolyte (MF batteries are bad about this.) will freeze, keep your face away from the battery. If all these check out use a Refractometer and check the specific gravity of the cells. IF there is a large difference between cells you have a bad battery, but it is always worth checking.

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I like cars.

It might be the battery, but, you won't know until you have it load tested. Don't throw money at a battery until you're sure.

The alternator is fine because the system voltage is above 13.5V when the engine is above 1500 rpm. These systems may not put out sufficient current at idle to keep the system above 12V. It's perfectly normal.