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Discussion Starter #1 (Edited)
Long story short.
Few days ago, the alternator crapped the bed in my VW, I drove until the battery died. Alternator is out being rebuilt now. I've been charging the battery for over 48hrs and the charging light (amber light) is on steady, on the Battery Tender Plus (1.25amp model). Sticking a meter on the battery terminals, I'm seeing 13.4v, with the charger disconnected, and it is rising at a steady, but slow pace. Surely it has to be at 80% charge by now, which should trigger the green light to turn, indicating a charge of 80%.
Is it normal to see 13.4v on a resting state battery, and it still not be charged (indicated not to be)? I'm still waiting on parts, so I won't be able to test starting the vehicle until next week sometime. I was able to start the vehicle on the side of the road, with a jump pack, but it died within a minute of removing the jump pack.

The battery is an 80ah battery.
There is no load on it, all connections to the vehicle are removed.
 

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I don’t have any figures, but...I’ve seen my Battery Tender take a really long time to charge a discharged battery. And that was with the standard version - a Jr will take even longer.

I would just trust the Tender to do its thing - be patient and wait for the lights.
 

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I don’t have any figures, but...I’ve seen my Battery Tender take a really long time to charge a discharged battery. And that was with the standard version - a Jr will take even longer.

I would just trust the Tender to do its thing - be patient and wait for the lights.
Right on. The Battery Tender is a battery maintainer, not a battery charger. If you have a depleted battery it can take a long time to bring it to full charge. This is especially true for the “Junior” unit. Battery Tender does make units will can deliver higher charge current. I think Deltran recommends charging a depleted battery with a conventional charger prior to using the maintainer.
 

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I have a deep cycle battery that runs the hydro pump on my dump trailer. I use a 40 amp charger on that and if I let the battery die completely it takes almost a full 24 hours to fully charge it back up again. A 1.25 amp trickle charger is going to take a heck of a lot longer than a 40 amp charger.
 

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I had the battery on the 3520 crap out this spring.
I put the Battery Tender+ on it and in very short time the green light came on and it measured 13+VDC or so. Removed the Tender and hit the key,.....click, click click....dead. Time to replace the battery :-(
 

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Discussion Starter #6 (Edited)
Right on. The Battery Tender is a battery maintainer, not a battery charger. If you have a depleted battery it can take a long time to bring it to full charge. This is especially true for the “Junior” unit. Battery Tender does make units will can deliver higher charge current. I think Deltran recommends charging a depleted battery with a conventional charger prior to using the maintainer.

It actually says Battery Charger and Maintainer, on the units front label. I'd have to say it's a charger as well.

I'm gonna let it go until tomorrow afternoon, another 24hrs or so. Maybe I need to add some water to it.

My real question was about it showing the 13.4v in a no load static situation.
 

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It actually says Battery Charger and Maintainer, on the units front label. I'd have to say it's a charger as well.

I'm gonna let it go until tomorrow afternoon, another 24hrs or so. Maybe I need to add some water to it.

My real question was about it showing the 13.4v in a no load static situation.
Yes, you are correct. They do consider it a charger, albeit a very slow one. Deltran has this note in the BT Plus manual:

"TIME REQUIRED TO CHARGE A BATTERY:The Battery Tender® Plus charges at a rate of 1.25 Amps, or 1.25 AmpHours per hour. Therefore, a fully discharged 15 Amp-Hour battery willtake approximately 10 hours to recharge to 80% capacity.

As a frame of reference, a fully charged 12-Volt, Lead-Acidbattery will have a rest-state, no-load voltage of approximately 12.9 volts.A fully discharged 12-Volt, Lead-Acid battery will have a rest-state, no-loadvoltage of approximately 11.4 volts. That means that a voltage change ofonly 1.5 volts represents the full range of charge 0% to 100% on a 12-Volt,Lead-Acid battery. Depending on the manufacturer, and the age of thebattery, the specific voltages will vary by a few tenths of a volt, but the 1.5-volt range will still be a good indicator of the battery charge %."

Lead acid batteries (Gel, AGM, Flooded, Drycell, etc) are made up of a series of 2.2 volt cells that are bridged together in series to reach their final desired voltage. For instance, a 6 volt battery will have 3 cells (3 x2.2= 6.6 volts), a 12 volt battery will have 6 cells (6 x2.2=13.2 volts) and so on.That 2.2 volts is the fully charged, straight off the charger number. The actual resting voltage, or the voltage a battery will settle at 12-24 hours after being removed from the charger, is closer to 2.1 volts per cell, or about 6.4 volts for a 6v battery, and 12.7 volts for a 12v battery. These numbers assume 100% healthy cells, and may vary a bit lower for older batteries.

The voltage you are seeing seems a bit high for a 12V battery. No load voltages can be tricky. Do you have a load you can apply to it like an old car headlight bulb or something? Putting a few amps of load on it and measuring the voltage will be more meaningful.

Given the history, odds are the battery is shot.
 

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Discussion Starter #8
Yup, I have the owners manual for this unit. Reads, just like you quoted. The 12.9v they mention, in the manual versus the 13.4v I am seeing, is what had me questioning what was up. What they should mention in the manual (and they don't), is the other info you posted about no load voltage testing 12-24hrs after removing the charger, to get a more accurate reading. I found that on the Battery University site too.

Low and behold, when I got home this evening, the amber light is solid, and the green light is flashing, indicating the charge of the battery, is 80% or more and everything seems to be hunky dory. Tomorrow hopefully, it should be solid green only, indicating 100-103% charged, and in float mode.

Woot:bigthumb:
 

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Discussion Starter #9
Just went out and checked it, its solid green.
I don't know what time it turned solid green, but it was atleast 72hrs of continuous charge time to get it there. I put it on Wednesday afternoon.
Next time, I will measure voltage before I start a charge cycle, during, and after. I should have atleast checked it before, this time.
 

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Just went out and checked it, its solid green.
I don't know what time it turned solid green, but it was atleast 72hrs of continuous charge time to get it there. I put it on Wednesday afternoon.
Next time, I will measure voltage before I start a charge cycle, during, and after. I should have atleast checked it before, this time.
Don't forget to measure the battery voltage while cranking the engine. Other than using a load tester, that should give you a better indication of the health of the battery.
 

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Discussion Starter #11
Don't forget to measure the battery voltage while cranking the engine. Other than using a load tester, that should give you a better indication of the health of the battery.

Good idea. Hopefully I'll have it back together tomorrow.
 

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Good idea. Hopefully I'll have it back together tomorrow.
If you can test the voltage at the starter it will tell you if the cables are good and clean. If Low then go back on the wiring till you find the problem. Might drop as low as 7-10 volts on starting not sure?
 

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Simple math,,
look at the battery, find the amp-hours,, for the VW it should be 600 minimum,,

divide the 600 by the charging rate,, (a trickle charger is 1.25 amps) ,, you get the hours to charge from full discharge.
half discharged = divide hours in half,,

so to charge a half discharged VW battery,,

600(guess) / 2,, = 300,,, 300 divided by 1.25 = 240 hours,,, or ten days
Get a 12.5 amp charger,, it will still take a full 24 hours.
Get a 25 amp charger,, = 12 hours,,
 

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Discussion Starter #14
If you can test the voltage at the starter it will tell you if the cables are good and clean. If Low then go back on the wiring till you find the problem. Might drop as low as 7-10 volts on starting not sure?
Oh yeah, I know all connections and cables are good. I just went through the whole system (all connections and cables) 2-3months ago, when I had the starter rebuilt, due to a faulty starter solenoid.
 

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Discussion Starter #15
Simple math,,
look at the battery, find the amp-hours,, for the VW it should be 600 minimum,,

divide the 600 by the charging rate,, (a trickle charger is 1.25 amps) ,, you get the hours to charge from full discharge.
half discharged = divide hours in half,,

so to charge a half discharged VW battery,,

600(guess) / 2,, = 300,,, 300 divided by 1.25 = 240 hours,,, or ten days
Get a 12.5 amp charger,, it will still take a full 24 hours.
Get a 25 amp charger,, = 12 hours,,

Absolutely but only kind of really, if, you know the variables. Like starting voltage when charging begins. Can't just guess.
 

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A battery load tester is an extremely handy tool to own for such issues are you are facing. First, it actually load tests the battery with the flick of the switch as many, if not most, 12 volt vehicle batteries will show 12.9 to 14.3 volts but with a bad cell, the moment a real load is put on them to start, the batteries are unable to start the vehicle or device.

The battery load tester also indicates the charging system output when the vehicle is running, which is very helpful to know. For the low cost of these tools, everyone who owns vehicles with 12 volt batteries should have one. It sure is easier than pulling the battery and dragging it down to Auto Zone or O'Reilly's, etc for them to perform the very same test you can do with the load tester.....

I have the Schumaker brand tester shown below and its a very nice unit. It's just under $50. You can buy a version from Harbor Freight which will also test for about half the price. It's not assembled with the same attention to detail but it works. Either way, one of these tells you more about the battery, the charging circuit and the 12 volt system with one connection than you can get with a voltmeter, etc...........



Amazon.com: Schumacher BT-100 100A Battery Load Tester and Voltmeter: Automotive
 

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Discussion Starter #17
Sulley, I will look into that, I didn't know they could be had that cheap, thanks.

Got it all buttoned back up today. The Germans way over engineer things, in some places.
Fired right up, first wick. Battery seems to be fine, and all is well on the home front. 250,305 miles strong, feels nice and smooth.
 

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Sulley, I will look into that, I didn't know they could be had that cheap, thanks.

Got it all buttoned back up today. The Germans way over engineer things, in some places.
Fired right up, first wick. Battery seems to be fine, and all is well on the home front. 250,305 miles strong, feels nice and smooth.
I have the one from Harbor Freight. It is normally $19.99 but I got mine for $14.99 with a 25% coupon. You can't beat that. I've looked at the Schumacher version and it is very similar. I think the HF one is actually built better as it uses a metal toggle switch instead of a plastic rocker switch.
 

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I have the one from Harbor Freight. It is normally $19.99 but I got mine for $14.99 with a 25% coupon. You can't beat that. I've looked at the Schumacher version and it is very similar. I think the HF one is actually built better as it uses a metal toggle switch instead of a plastic rocker switch.
They are so handy to have on hand. Any time you have a doubt about a battery it just takes seconds to do a load test.

I also check all my batteries going into winter to be sure they are up to snuff.
 
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