Hello again.
I have an electrical problem where the battery voltage is 13.5 with the engine running (thanks to a new alternator, newish battery) but when I shut it off it drops to 11.5, barely enough to start it again. And then the next morning it's always back down to 10.5!

Nothing really remarkable about my electrical system except that there's no driver side headlight (anyone got one for $40 or so?) and my blower motor is on the fritz. And I think I have a bulb out somewhere. But I pulled the fuses for each of those things, and still the voltage drop.

To get around this I've been using a battery tender. It's the first ever 240 plug-in hybrid! But seriously, this is pretty inconvenient.

First step, charge the battery and disconnect it. If it still has its charge in the morning, then you know the battery is okay and that there is a current drain.

If so, have the doors locks been acting up? A shorted door lock wire is a common cause for rapid battery drain.
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1980 245 Canadian B21A with SU carb, M46 trans, 3:31 dif, in Brampton, Ont.

^^
Yes, yes.
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Art Benstein near Baltimore

Whereas 12.6 v represents 100% charge (after being allowed to sit for a few hours since charging), 11.9 v represents 0% charge. Your 11.5 v tells me the battery is virtually dead. However, the cause is the issue, so lets look into this...

Usually, when a battery is bad, the charging (engine running) voltage tends to be higher. That your engine-running voltage is around 13.5 suggests (although not a confident indicator) that your problem is elsewhere.

First, of course, check your cables for corrosion -- that might be the reason the battery isn't charging higher.

Beyond that, you want to consider an abnormal battery drain. I assume you have a VOM (digital or analog). To start the search, remove the negative cable (always disconnect the negative cable first, and reattach the negative cable last) and put your VOM probes between the negative cable and the negative battery post.
The normal battery drain for a stock 1990 240 is 12 milliamps (0.012 amps) with brief pulses to 25 ma (.025 amps) to drive the clock's motor. 2.8 ma of that 7.8 is for the radio's presets, so if you changed the radio, these figures would be different. And if you swapped out your clock for a large tach without installing the small 2" clock instead, the normal drain is a steady 7.8 ma (0.0078 amps).

If you've got more amperage than that, you have to search further. Restore the negative cable connection to the battery, and then go to the fusebox. For each fuse, pulling them one at a time, put your VOM probes across each set of contacts and search for the abnormal battery drain. You should find the problematic circuit; and then you have to check all the components of that circuit.

Folks will offer suggestions: e.g., the electric door locks is a common problem, for example. Consider these as possibilities.

After you've found the problem, you have to check your battery to see how much it's been damaged by the severe discharge (batteries are severely damaged, e.g., sulfation, when their voltage drops below 50% for extended periods).
The best way is by measuring the specific gravity of each cell (you can buy a tester in an automotive supply store) -- 1.265 is ideally fully charged, whereas 1.100 is completely depleted. Remember to fill, if necessary (and then recharge before testing), with distilled water.

If you don't check specific gravity, you can check each cell for voltage. Pull all the caps and then use your VOM to measure individual pairs of cells. Start with a voltage reading between the positive (or negative) terminal and that end's cell by sticking one probe on the terminal and then the other probe inserted in the adjacent cell's solution (but not deep enough to touch the plates in the cell). Then progress with probes dipped into each adjacent pair of cells, successively progressing toward the opposite battery terminal. Each pair of cells ideally should show 2.1 volts at full health; and 1.99 volts is "dead"; but remember that the battery terminal-cell pairing at each end should be roughly half that. This assumes, of course, pretty good accuracy of your VOM.

Good luck.

there's nothing aftermarket in the car and the stereo is unplugged.

the current drop across the negative post and the negative battery cable is 40 mA so from what you're saying it seems like a parasitic drain. I will have to check the individual circuits later.

the battery is making gurgling sounds by the way. It's a Die Hard Gold so I'll take it back to Sears, but I suspect they're going to get it back up to 12 volts and then claim that it's fine >:(

40 ma is not that serious, and assuming it's a more or less accurate figure (within the tolerance of your VOM), I'd say that there's another issue at work. Consider that the glove box or dome light bulb (if you left the door open) will drain more than this, and your battery if healthy should easily tolerate this overnight.

I'm thinking that your battery is toast. You mentioned that you just rehab'd your alternator -- I think that the history of your battery suffering from poor charging prior to that repair might have caused irreparable damage, so that now it just can't hold a charge for long (i.e., overnight). Remember that I wrote earlier that a battery left below 50% for long periods will become sulfated -- I'm thinking that this happened.

You can try to have it charged properly using a multi-phase charging regimen, but I don't think it will restore the battery.

In addition to my suggestions (e.g., checking the individual cells for specific gravity) and someone else's, too (e.g., a load test), I think you'll discover that the battery just isn't up to the task anymore.

Ken, I think you are right on in this one.

In your previous post, I was looking to see you suggest the OP disconnects the battery after taking that 11.9V reading, and re-measuring it the next morning before connecting it again. If 10.5V or thereabouts, I think you would have been able to clinch your diagnosis then. One cell is shorted.

By the way, with the Bosch system, there is no exact voltage to expect while charging a battery without defects, e.g. the 14.0 nominal claimed on the regulator. The EL-1 regulator adjusts this voltage around nominal using a thermistor to detect ambient. When Bosch designed this, I think they did not expect the internal EL-1 to be used in the ambiance underneath the exhaust manifold. No telling how this works with rebuilt and aftermarket alternators, but if we see 13V at least we know the battery is getting charged, at whatever rate.














--
Art Benstein near Baltimore

Those who jump off a Paris bridge are in Seine.

Yes, charging voltage is temperature dependent. In all my Volvo green books, even going back to my 1973 164E, the sections on charging systems have always shown a graph depicting charging voltage vs temperature (i.e., colder temperature means a higher voltage).

Clearly, you can see this if you have a dash instrument voltmeter, as the initial (when the car is started in the morning) voltage in winter is always noticeable higher than in summer. I've always thought that this design was to accommodate the needs of the battery.

And as you pointed out, I've always laughed at the idea that the sensing thermistor is embedded in the alternator case (which happens to be under the exhaust manifold), as it should instead be remotely located in beside the battery.

In fact, this is exactly the case with high-end battery charging systems in cruising sailboats. Because these carry huge battery banks costing thousands of dollars (and are also extremely heavy and cumbersome to replace), they are given the utmost care, and the charging systems on the auxiliary engine's alternators (i.e., often more than one alternator) have remote temperature sensors that are attached to the batteries in the battery bank. Even though they're not close to the hot engine, cruisers traveling annually from temperate areas to the tropics ("snowbirds") can see as much as an 60+ degree F change in ambient conditions in the hold, and this effects the proper charging voltage.
All of this, by the way, in addition to additional electronic controls on the alternator output to facilitate multi-phase charging regimens -- nothing is too good for their batteries because these sailing cruisers are so dependent on them.

Along with everything Ken C wrote I'd add---have the battery charged by a shop type charger and then use a load tester to check its condition. "Newish" or not you can't discount the possibility of the battery being bad. -- Dave

Yes! Before I spent very much time on chasing things, I'd have the battery fully charged and then take it to a good shop or parts place that has an electronic tester. It wouldn't be the first battery out there that's defective brand new out of the box, so to speak..

Alternator should be putting out 14.5 at least upon startup 13.5 is not enough to charge sufficiently. Sure sounds like a bad battery.

I have had a few weirds problem w my 740t,,after total frustration I got a ride to Autozone,,& took the 5mo.old battery in & it was dead again,,
They said thatall the battery factories moved to Mexico & quality went w it,,,,this is the 3rd battery I have replaced under warranty for the last 8 mos.