Elmiko

I'm using a Deltran Battery Tender Junior this winter. I had planned to leave it plugged in pretty much for the winter months, but the Tech Talk column author in the last Porsche Excellence says he thinks it's dangerous. The unit runs nice and cool, and I thought it was designed for continuous use during winter storage. Does anyone else just leave it on and forget about it?

pcar928fan

"Tenders" should be fine. They are designed to turn off and on based on current voltage of the battery, so when it drops the tender comes on...

I have used them on my '92 and '82 successfully for years.

Alan

Would rather defeat the point if you didn't leave it on right...?

Alan

jayc67

"Dangerous" for what?

For winter storage I leave mine on BUT I disconnect the battery ground so the battery is isolated.

I no longer use the under hood power points, having just replaced my LH brain. After that little jewel my paranoia is in high gear.

the flyin' scotsman

Despite what 'they' say I always bring my battery indoors during the winter months. My garage and quonset are not heated so although the batt. could be on a tender/charger out there IMHO the warmer climes of the basement do its life service well.

Yes, its on a tender............Dec thru Mar/Apr

pcar928fan

Alan,

I am not sure what you are saying...

The "tender" is always plugged in and connected to the car battery when the car is parked inside the garage... so it is always "on" but there is no current being delivered to the battery unless the voltage drops... This is a HUGE difference vs. a battery charger that when turned on will continue to deliver charge regardless of the battery's condition. What that can and does lead to is a battery explosion! NOT FUN...not fun to clean up either! I am not saying that is the only way batteries blow up mind you, but it is MUCH more likely to cause a failure than a "tender"... A friend had his battery blow up in his Carerra GT (it was on a charger or a tender, not sure which) with 29 miles on it... did over $20k worth of damage to the car and I suspect ruined his "investment" in the process...

jacal128

You can't predict a failure in the tender, but between the unit and the electrical system ( up to code ) it is very safe to leave plugged in.

j.kenzie@sbcglobal.net

My Schumacher tender says not to leave unit connected to battery when not plugged into 120V ac. This is a different question, but why do you suppose they give that warning. It would be convenient to tuck the tender into the trunk and just leave the plug accessible.

tveltman

Short through the unprotected plug maybe? Also product liability lawyers probably are simply trying to dodge a bullet there

pcar928fan

Ultimately it could drain the battery too...

the flyin' scotsman

We dodge the liabilty folks with large calibers.............to many folks down there.

Elmiko

Actually, Deltran (the manufacturer) doesn't warn about leaving the tender plugged in and connected all winter-it was the writer of the Tech Notes column in the current edition of Porsche Excellence. Someone asked about storing his car in an unheated garage with the tender connected, and Tech Notes recommended taking the battery out and keeping it inside where it's warm, connected to the tender. I don't remember all the reasons, but one of them was that he doesn't think they're safe to leave on 24/7. I can't find the issue right now, else I'd quote it exactly.

JPTL

A product specifically designed as a trickle charger/maintainer should be fine keep connected on the battery for extended periods of time. Of course removing the battery from the car is a good safety measure. Manual chargers should never be used to maintain a battery past its charge. For long term storage/maintenance, automatic chargers should also be disconnected at full charge and replaced with a trickle charger/maintainer.
One rule of thumb to ensure proper operation of a charger with a tender/maintainer feature is to keep the original alligator clips intact and connect directly to the battery &/or ground point. Avoid using a pigtail or extension which can be more convenient but more dangerous.

I've found that changing the resistance of the wiring connected to the battery to something other than that of the charger's original wiring changes the reading (resistance?) that some chargers rely on.
This was my experience:
For convenience, I installed a pigtail connection to maintain the 928 battery, in-car. It was a decent gauge wire, but higher gauge/thinner than that of the charger's wires. For some reason, the Schumacher charger/maintainer sensed that the battery needed charging, even though it was fully charged. It gave the battery a steady 2 amp charge and the acid reached a boiling point.
Fortunately I smelled it and disconnected the charger (after airing out the hatch & unplugging it first). I thought that it was a faulty battery, and tried the same thing on the pigtail for my motorcycle battery. It started to boil that one as well. This charger/maintainer works fine when directly connected via its alligator clips and senses a fully charged battery. Since it has a 10 amp fast charge option as well as a desulfator feature, I'm guessing that it was getting a false reading as a result of my pigtail mods. I have no idea whether it was cycling through desulfator mode or simply giving the battery the amps that it thought it needed. I've noticed that Schumacher no longer offers chargers with a desulfator feature. Maybe they had similar problems with these. Regardless, my pigtail mod. was a very dangerous situation.
Lesson learned.

Alan

Well he's an idiot - THAT IS THE WHOLE POINT... keep it plugged in - a fully charged battery will not freeze down to about -70C while a fully discharged battery may freeze at -10C. A battery that frezes will likely be destroyed. A significantly discharged battery will also quickly degrade... so keep them charged - to do thaqt it has to stay plugged in...

A warm battery will work much better than a cold one to start the car - however cold itself does no significant harm as long as you avoid freezing & discharge. By all means bring them in to a warmer place - but its not a real requirement... eventually you have to put the warm battery back in the car - its pretty soon going to be cold again... unless you'll keep it out all winter...

Moot point for me...

Alan

Alan

I thought I was pretty clear - connect it to the battery and leave it plugged in...

As you say a maintainer or tender is designed to regulate itself and charge only as needed. It is designed to be always on - this certainly does it no harm nor the battery any harm...

Agreed a medium/high rate charger is a different matter - temporary use only.

However this thread was specific to battery tenders...

Alan