Battery Tender shows battery less than 80% charged for days

For about the last 3 weeks I have parked the passat (SEL if that matters) in the garage that is always about 50 degrees. After reading about the issues of maybe leaving the car parked unlocked and the rsn-510 maybe using some power, I decided to hook up the battery tender.

I opened the hood and pulled back the flap over the battery. I hooked the tender up directly to the battery. The light on the tender has been red for four days. That seems very odd as I would think it would be above 80% after 12 hours.

Is there a draw on the battery that might make it act like this or?

I started the car and it started great and my volt meter shows 13 volts? I can put the tender on my jeep battery and it shows fully charged.

Be careful with that tender is all I'd say Get a different one @ Wally and try it for a few days (can always return it) to get a "second opinion"

I just returned a Battery Tender to the manufacturer after it boiled 2 batteries dry (RV deepcycle batteries). I'm waiting to hear from them why it never stopped charging.
I would agree, at this point, with r11.

It maybe that the VW battery is too low on charge as the battery tender is not designed to charge a battery in the way that a conventional battery charger is made to do. The voltage in the battery is not an accurate way to determine the "fullness" of the battery.

I'd suggest you take the car out and drive it for a few hours and then hook up the battery minder to see if it stays on red after more than one hour. If so, there is probably an issue with your battery since it is on green when you attach it to your other vehicle. If, not return the battery minder for a replacement. (I had one that wouldn't charge, so I sent it in under warranty. The fuse had blown and I was told that it would not charge a dead or depleated battery..thus the blown fuse.)

Then again the battery 'tender" maybe a different unit that the batter "minder," of which I have several. (minder.)

I'm happy to see a thread on battery tenders. I've been wondering if the BMW battery tender I have that was designed to plug into the cigarette lighter socket to trickle charge the car would be adapatible for the PASSAT. It certainly was an elegant sollution and absolutely mandatory with the BMW, as their native systems always were eating electrons.
Any EEs out there that can offer an answer?

To clarify, mine was a "Battery Tender Plus", 1.25 amp. The dealer where I purchased it says he trusts them less and less.

remember that for a lighter socket tender to work, the socket has to be "always on" type. Most sockets are only connected to the battery when key is in and turned to at least position 1.

Some cars have 2 sockets - one of which is always-on type. Like my Cherokee

If you park outside, I most highly recommend solar trickle chargers - like the $15 (item #68692 ) item from Harbor Freight. A total no-brainer to use and you never have to worry about dead battery.

Mine is a Battery Tender Jr. I have used it for many years without issue.

I will pull it off and let the cards fall where they may. I hope in a month or so to be driving the TDI again.

tdiatlast said:

I just returned a Battery Tender to the manufacturer after it boiled 2 batteries dry (RV deepcycle batteries). I'm waiting to hear from them why it never stopped charging.
I would agree, at this point, with r11.

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Phone call from Battery Tender today. They are replacing my 6 year old BatteryTenderPlus at no charge, (they wouldn't tell me what part had failed) and sending me a check for $100. I did not request more $$$ because, in all fairness, the first battery was over a year old, out in the sun 24/7...I should have been monitoring the electrolyte level, and would have caught the problem earlier. The 2nd battery was only a few weeks old, boiled dry.

They did tell me that, as the unit is a maintenance charger, I only need to check electrolyte levels every 2-3 months, NOT the "every 30 days" that is stated in the brochure.

I'm pleased with their attentiveness, and their willingness to honor their 10-year warranty.

I have 3 "Battery Tender" brand and 1 C-Tek battery maintainer. Owned the "Battery Tender" brand the longest...6-9years no issues at all..I've owned 2 C-teks...one died after 1 year and exchanged it for a "Battery Tender". Are you by chance unlocking your car/entering the car before looking at the battery tender? If so that would trigger the 80% LED...interior lights coming on is enough draw to switch the Battery Tender from float mode to charge.

No unlocking or locking. Just opening the hood and hooking it up. It went 3 days in the red and never got to the blinking green or 80%.

rustycat said:

I'm happy to see a thread on battery tenders. I've been wondering if the BMW battery tender I have that was designed to plug into the cigarette lighter socket to trickle charge the car would be adapatible for the PASSAT. It certainly was an elegant sollution and absolutely mandatory with the BMW, as their native systems always were eating electrons.
Any EEs out there that can offer an answer?

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Works beautifully on my S4 and MKV Jetta, both with hot sockets.

I find that if the battery charge is very low the battery tender will not work. Does as you describe. When I've encountered that situation, I attached the battery to a regular charger and charged 10-12 hrs. That got the battery charged enough where the battery tender would work and than could fully charge the battery over the next 24-48 hours.

A lot of chargers now days won't turn on for a very discharged battery. IIRC it looks like a dead short (touched the leads to each other) so the charger doesn't come on to protect itself. Putting another better charged battery inline with it will allow the charger to come on and once it gets some charge the other good battery can be removed. Might be worth a try.

tdiatlast said:

Phone call from Battery Tender today. They are replacing my 6 year old BatteryTenderPlus at no charge, (they wouldn't tell me what part had failed) and sending me a check for $100. I did not request more $$$ because, in all fairness, the first battery was over a year old, out in the sun 24/7...I should have been monitoring the electrolyte level, and would have caught the problem earlier. The 2nd battery was only a few weeks old, boiled dry.

They did tell me that, as the unit is a maintenance charger, I only need to check electrolyte levels every 2-3 months, NOT the "every 30 days" that is stated in the brochure.

I'm pleased with their attentiveness, and their willingness to honor their 10-year warranty.

Click to expand...

Just to follow up...received the new 1.25 amp Battery Tender replacement today, with a check for $100. They were true to their word!
Hopefully no more boiled battery for me (all of this on my popup trailer, NOT on the Passsat...)