Battery Tender Issues

Archrms · #1 (**permalink**) 02-18-2014, 12:29 PM

I have battery tenders on the Cobra, a 1966 Mustang, and a motorcycle. The tenders have been on the Mustang and motorcycle for years with no issues. Last year I noticed a bad egg smell in the garage one day and traced it to the trunk of the Cobra. The battery was fried. It was the original battery so I figured it had just gone bad.

Got a new battery, and hooked up the tender. A few months later, I noticed the smell again. Drove it to the store where I purchased the battery. It was red hot by the time I got there, where they confirmed that it was fried. They gave me lip about replacing the battery so soon under warranty, and said they would not replace it again.

I threw the battery tender on the Cobra out and hooked up the one that has been on the Mustang. Less than two months later the smell was coming from the trunk of the Cobra again. I have not had it tested, but it is likely fried again.

What could be causing the batteries to be fried one after the other while on the battery tenders? I have used two different battery tenders with the same results. I have replaced the Ammeter with a Voltmeter, which was showing normal voltage before being garaged for the winter.

DAVID GAGNARD · #2 (**permalink**) 02-18-2014, 01:01 PM

Quote:

Originally Posted by Archrms

I have battery tenders on the Cobra, a 1966 Mustang, and a motorcycle. The tenders have been on the Mustang and motorcycle for years with no issues. Last year I noticed a bad egg smell in the garage one day and traced it to the trunk of the Cobra. The battery was fried. It was the original battery so I figured it had just gone bad.

Got a new battery, and hooked up the tender. A few months later, I noticed the smell again. Drove it to the store where I purchased the battery. It was red hot by the time I got there, where they confirmed that it was fried. They gave me lip about replacing the battery so soon under warranty, and said they would not replace it again.

I threw the battery tender on the Cobra out and hooked up the one that has been on the Mustang. Less than two months later the smell was coming from the trunk of the Cobra again. I have not had it tested, but it is likely fried again.

What could be causing the batteries to be fried one after the other while on the battery tenders? I have used two different battery tenders with the same results. I have replaced the Ammeter with a Voltmeter, which was showing normal voltage before being garaged for the winter.

I'm not an electrician by any stretch, but I always dis-connect the positive cable on my battery if I don't plan on driving the car for more than a couple of weeks and have had no issues with batteries/tenders....had one Optima battery last 7 or 8 years this way....

xb-60 · #3 (**permalink**) 02-18-2014, 01:23 PM

I'm with David on this. I have a quick disconnect on the positive terminal, and batteries now last much longer. The car sometimes sits unused for a few months at a time, but there's plenty of kick in the battery after that time to pump fuel through and start. I periodically think of buying a tender, but each time I talk myself out of it because I wouldn't get any advantage by using one.
Cheers,
Glen

601HP · #4 (**permalink**) 02-18-2014, 01:48 PM

I'm curious as to your root problem. I don't have a suggestion. I have 3 vehicles. Each has a battery minder attached. All aren't connected in the same manner.

a. The Cobra: the positive cable is always switched off when sitting. Same battery for about 7 years.
b. The F350 diesel: it has twin batteries. All cables remain connected. Same batteries for about 3 years.
c. The Mustang: All cables remained connected. Same battery for about 5 years. (sold this car last month)

David

joyridin' · #5 (**permalink**) 02-18-2014, 02:37 PM

I have a battery disconnect switch and the car/battery has been sitting 4 years now. I started it in October with no problems. The battery is probably 6-7 years old. My bike sits all Winter in the garage without a tender and the battery is 4 years old now with no problems.

Unless your garage gets below freezing on a regular basis or the car/battery has some type of drain on it, using tenders really doesn't help.

MOTORHEAD · #6 (**permalink**) 02-18-2014, 03:21 PM

Get a voltmeter (VOM) across the batt terminals when the tender is hooked up and monitor the voltage periodically.
If less than 12, the charger isn't doing its job. but thats not going to "fry" the battery. look for too high voltage (14 + volts) But the same tender works ok on other vehicle.
Need to check charging voltage. First step to figure out whats going on. If voltage is too high or low, disconnect either cable from batt and re-test with VOM.
First guess is car wiring problem. Don't know the wiring on SPF's, Blas has diagrams if you don't, but the nature of these cars is that strange mods by previous owners is always a possibility !

Xack · #7 (**permalink**) 02-18-2014, 05:02 PM

The common item is your wiring. Different tenders, different batteries. Chances are your first battery tender is still good. All else being the same, you should buy a disconnect and switch on the -(Negative). The switch makers suggest you switch your -(Negative) side since your switch at zero volts does not arc when switched on or off. Arcing causes oxidation and burned contacts which shorten the life of your device.

DanEC · #8 (**permalink**) 02-18-2014, 05:09 PM

I've read too many horror stories about batteries blowing up - apparently from being left on a battery tenders. I use disconnects on my old cars and the batteries stay charged and batteries last a good long time.

Archrms · #9 (**permalink**) 02-18-2014, 07:06 PM

I agree with Xack, in that the common item is the Cobra. However, I had no issues with the battery (the original battery lasted five years) before using the tender on it. After hooking up the tender, it keeps frying batteries every few months. It may be easier to just disconnect the battery as suggested and stop using the tender, as it seems to be causing more problems than it is worth.

awfink55 · #10 (**permalink**) 02-21-2014, 04:54 PM

Archrms, Your battery problem is unusual and a concern. I use a battery tender on my Cobra and 2 other cars without a problem. So, you may want to disconnect both battery cables from the battery and then put the tender on the battery. This isolates the battery from the car. If the battery keeps the charge and does not overcharge and heat up, then, your problem is related to the car to battery relationship and further investigation is necessary. Hope this is helpful.

Trueoo7 · #11 (**permalink**) 02-21-2014, 08:25 PM

I would look into a "Battery Tender" (that's the name) from Deltran. www.batterytender.com
Its the only one I would use. If you look on their site there is a lot of info about how a battery is charged and what happens when it is hooked up to their charger. More info then I ever knew. A little more expensive but well worth it. I've had mine about 8 years and have charged dozens of batteries with no problems whatsoever. I am currently charging 6 - 6 volt batteries for my golf cart with it. Its the smartest way to go if you are going to keep batteries charged.

Ron61 · #12 (**permalink**) 02-22-2014, 03:37 AM

I have used the Deltran Battery Tenders on 3 cars for years and no problems. I do have my disconnect switch on the Negative side of the battery in the 69 Cobra and I had to replace that battery last summer and it was 14 years old.

awfink55s suggestion of disconnecting the battery completely and seeing if it happens is a good one. If the battery is over charging, then something is causing the tender/charger to try to charge it. Possible a small short somewhere in the cable or something is drawing a little current all the time.

Ron