Leaving battery tender unattended?

[bob15]

NO thanks. Not for me. Google "garage fires caused by battery charger". There are 19 million results from that Google search. Granted not every article is about a different fire, but here's just one article:

https://www.hagerty.com/articles-videos/articles/2017/03/28/burned-out-bikes

Did you read the article? You are comparing a battery charger to a battery tender/maintainer.

It says: Editor's note: A previous version of this article described the battery charger referenced in the above article as a “battery tender.” It has been brought to our attention that Battery Tender is a registered trademark of Deltran. Hagerty has no reason to believe that Battery Tender branded chargers are unsafe or were the cause of the aforementioned fire.

It also says: Stick to “smart chargers,” which shut off automatically whenever the battery is full and turn back on when they sense a drop in voltage. They also shut off whenever a short is detected. If you don’t have a smart charger, unplug it if it will be left unattended for an extended period.

Do you leave your refrigerator, freezer, oven and microwave plugged in......among all the other appliances in your house?

 

[lakeroadster]

I'm with Bob

 

[Hilltopmasonry]

Do you leave your refrigerator, freezer, oven and microwave plugged in......among all the other appliances in your house?

Yes I leave them plugged in but they are on a timer.....




Haha sorry I couldn’t resist



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[PMD1966]

Battery Tender Junior. One for my old Jeep. One for my garden tractor. No problems after 6 years.

 

[HOTFR8]

Using the term battery tender, generically, can lead to confusion. The name rightfully belongs to the Deltran series of small multistep chargers that charge at .75 to1.25 amps and charge at constant current, then constant voltage and then float charge. A battery can stay on them indefinitely. The term is often applied to cheap trickle chargers that charge at constant low current and in time will boil a battery dry. However, there are other good "tenders" like the C-tech that are safe for continuous use. I just replaced a battery that lasted 11 years on a 1.25 amp Battery Tender Plus. All little battery minders are not Battery Tenders.

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I have sold both the Deltrans units (Sold as Matson now Tridon in Australia) and the C-Teks. I have also had batteries last for longer than 11 years when they are usually scrapped after 3 years the average life of a car battery. I have seen many a cheap trickle charger fail to the point of melt down of the charger. Plenty of quality brand tender - maintainers on the market and these days the difference as to a charger-maintainer-tender and a trickle charger is not explained at the point of sale.

 

[6PTsocket]

+1

I agree

Been using a tender for a few years when I store my 15 Camaro for winter and never had problem.

Older cars were ok to store for a while since there was no electronics in them but my Camaro will go dead after 3-4 weeks. Don’t know if that normal or not


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A modern car should only draw about 25 ma on standby, to carry the computer and radio settings. Either you have a parasitic leak or your battery is shot. It should start after a lot longer than a few weeks.

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[bob15]

Yes I leave them plugged in but they are on a timer.....

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What is really scary is there are probably people out there that do just that.......... put them on a timer

 

[HOTFR8]

Timers and trickle chargers are simply an accident waiting to happen.

 

[ttpete]

I like the Battery Tender brand. But there are 2 reasons I won't leave unattended.

I had an moderately priced motomaster intelligent timer hooked up to a Suzuki cappuccino, sure the battery is on the smaller side but still somehow the battery vented in an attached enclosed garage. Not sure if a charger or car issue, I don't dare use this charger anymore. The hydrogen sulphide produced is toxic, hydrogen gas is also explosive.

The 2nd reason, I primarily ran either a full sized motomaster charging rig with maintain function or a Schumacher intelligent charger on my Grant National, I'm talking maintainer hooked up 365 days a year. Current and electrolysis in the cooling system to the point where a 200 miles(but 3years) water pump completely eroded through and leaked! After a lot of checking the only electrical short in the car is the oe stereo. I've since wired the stereo circuit to a switch and switched to distilled water. If I ever had to charge this car I suppose I would disconnect the battery as an added precaution.

So I have maybe 8 charger/maintainers that no longer see much use. I'll charge a battery only as needed, no more maintaining for me.

What you need to do is get rid of your antique flooded electrolyte batteries that gas off hydrogen and install AGM (absorbed glass mat) sealed batteries. They don't gas off or require water to be added.

I don't believe that a battery maintainer hooked directly to a battery can have any electrolytic effect on a cooling system.

I have a truck size AGM battery in my big generator that's been there for over 12 years and it still is in good shape. My motorcycle batteries are 9 and 8 years old and are fine. All are on tenders 24/7/365 when not in use.

 

[Greatbear]

Don't use a timer to cycle the power to a "Battery Tender" (battery maintainer/charger). The Deltrans and similar "smart" charger/maintainers all operate on a similar principle. When initially connected to a batter and powered up, the maintainer/charger will apply a current-limited charging voltage to the battery. Eventually, this voltage will reach about 14.5-14.7 volts as required by the battery to fully charge. The maintainer will hold this voltage until the battery draws very little current, indicating the battery is indeed properly charged. Once this happens, the maintainer will switch to a "float" value of about 13.2 volts. This is the "maintenance" charge. It's not high enough to cause the outgassing of electrolyte that causes early failure of batteries, but it is high enough to overcome any internal self discharging effects or external discharging current from the car/equipment the battery is installed in. As long as the maintainer is powered up, this float voltage remains applied to the battery unless the car is started or some electrical accessory (like interior lights, etc) is turned on and drops the battery voltage below a certain amount.

What does all this have to do with cycling the power to the charger/maintainer? When the power is turned off, the battery voltage will begin to drop, even if there is nothing drawing any current from it. If everything is up to snuff, the battery voltage will drop to about 12.8 volts and stay there. If you now power up the maintainer once again, it will start the charging cycle once again, going up to 14.5-14.7 volts, holding it until the current drops, then switching to float mode. The needless charging cycles over the float voltage can reduce battery life over time, especially in warmer climates and storage temperatures. The newer maintainers are best left plugged in all the time. They have protection circuits that will shut things down in event of failure or unusual circumstances, and they draw very little power from the line when "maintaining."

Older "trickle chargers" and so-called automatic chargers from 30 years ago don't work the same way as a true maintainer, they either deliver a lower current, unregulated charging voltage all the time which can be quite a bit more than the 14.7 volt cycle charge that the charging system of a vehicle operates with, or will shut off all charging after a full charge and either turning it back on when it drops to some certain value (usually 12.2 volts, considered as a "low" charge") and restarts the full charge cycle again, or just stays off. Either one not good for a battery in storage.