WTF??? Battery tender overcharging?

[pwd72s]

Is it possible for a battery tender to go bad? Here's the scenario:

Put the tender on the Mustang original battery last night. When I went to bed, the "Battery Tender plus" was giving me the solid red light with the green light flashing. According to their info, this means battery is 85% or better charged...

two lights...red & green. Solid red = charging. Solid red with green flashing = 85% or better charged. Solid green = fully charged.

So, this morn...light still red with flashing green. There was a power outage here, dunno how long. Thinking maybe a surge?

Anyway, left it on...but after a few hours, took the tender off, hooked up a Diehard automatic charger, set at automatic, 2 amps input. It's green light instantly read fully charged.

Unhooked it...multimeter reads 13.23 volts.

According to the chart with the Diehard, 12.67 volts is fully charged. This means the Diehard is set to shut off at that?

Further test was to then put the Battery Tender on the Ranger...it running a red top optima. Solid red, indicating charging. Unhooked the Battery tender, got a 12.89 reading on the Optima. Hooked Battery tender back up, it began red with flashing green after 1/2 hour or so...took another multimeter reading...12.98 volts this time.

As I type, still red with flashing green on the Ranger. Figure I'll leave the Battery Tender on a while, then test voltage again.

So, any thoughts? Time to buy another battery tender plus? This one is about 6 years old. I've been pretty happy with it's performance overall.

[Joe Bob]

The resting battery should drop a bit after you disconnect to under 13v. Put a meter on it, walk away....come back 15 minutes later....

The important number is what it's taking while being charged. Hook it back up and put the meter back on it. If it exceeds 14v and doesn't drop to a lower charge, you have a problem.

Anything over 14.5, 15v.......I would replace it or talk to the manufacturer.

[pwd72s]

Many thanks...will do!

[john70t]

On a fully charged lead-acid battery there is a surface charge(similar to static electricity) of 13-15V, and then there is the true chemical charge of around 12.6V.

The surface charge can be removed by loading it with 20-30 seconds of headlights/defroster/etc.


The alternator and charger need to run at a higher voltage(electric pressure) than the battery so amps "flow" towards the lower potential. You could use a multimeter to check what the voltage is at the charger posts before and after plugging it in.

[Joe Bob]

Aren't "tenders" designed to be "maintained" with the terminals connected?

[pwd72s]

Again, thanks guys...I think Joe Bob nailed it...after 1 hour or so of just sitting, Mustang battery down to 13.09...

Put the multitestor on the Battery tender as I was charging the Ranger's optima.
Battery post to post reading was 14.68! Yet it was showing flashing green

Just took it off...post to post: 12.86.

Going to replace the unit...

On the plus side, Battery Tenders cost a lot less than new batteries...

[pwd72s]

Originally Posted by Joe Bob

Aren't "tenders" designed to be "maintained" with the terminals connected?

Yes...AFAIK they are supposed to work with battery fully installed in the car, then shut off when good voltage is obtained.

My thinking is that my DieHard 12/2/75 amp fully automatic charger is still functioning as designed. It's the Battery Tender plus that I'm nervous about.

Like I said, we had a power outage when the Battery Tender was hooked up...maybe there was a surge when power came back on, damaging the unit???

(edit) A link to the Battery Tender website...there they say they use a microprocessor to control the charging. Maybe it blew when the power went back on?
http://www.batterytender.com/?gclid=CLzM6NSg7aUCFRtqgwodnhPNnQ

[Joe Bob]

Electronic chargers are supposed to have surge protectors and reset themselves in the event of an outage or a drunken stumble over the plug. If'n yer anal, plug it into a surge protected GFI style power strip.

Like I said, test the charge sequence with a Fluke. If it's outside the parameters in the specs listed in the stoopid book.....then *****hemoi to the manufacturer/replace it.

Send me the old one....%^b

[GH85Carrera]

It is just that Mustang. You should try it on a well set up 944!

[javadog]

I have been using the Battery Tender Junior model for years on all my cars and bikes. They work just fine, so there's no need to spend the extra dough for the bigger version.

One thing I will add is that you need to check the water level on any battery that has removeable caps. Even one of these chargers will deplete the water. Deplete it enough and you may have a battery explosion. Take my advice, you don't want to experience this first hand.

Some of the other battery types (I'm thinking of Optimas and the like) may do better with a different type of charger.

JR

[Noah930]

The guy who runs the Yahoo Ducati 851/888 list (he's a retired engineer, IIRC) has been harping for years on how the vast majority (almost all) of battery chargers out there aren't adequate. To be fully charged, batteries should actually be charged up to 14.4-14.6 volts. The charger may not float the battery at that level, but it should bring it up to that level before "floating." Apparently he's tested dozens of chargers over the years and hasn't found many he's fond of--including the Battery Tender series. You can't go by the charger manufacturers' claims, as they all say they fully charge a battery. You have to sit there with a voltmeter and watch what happens after you attach the charger to your battery.

Here are a couple he's recommended recently:

This Walmart one was $19 when I ordered it a month or two ago. Did as advertised an brought the voltage up to 14.6 or so within a few minutes of plugging it in to my bike, before floating back down to 13.7 or so. I have a voltmeter hardwired on the bike.
Walmart.com: Schumacher SpeedCharge Battery Maintainer and Charger: Automotive

6/12 Volt Electronic Battery Charger and Maintainer With LCD Display

[pwd72s]

More out of curiosity than anything, I'm going to get a new battery tender & send the old one to Joe Bob. He'll test it.

Heck, it might be just fine, but now I'm a bit spooked...

In either case, it's Joe Bob's now...

[Joe Bob]

Too bad I can't read....

[pwd72s]

Originally Posted by javadog

I have been using the Battery Tender Junior model for years on all my cars and bikes. They work just fine, so there's no need to spend the extra dough for the bigger version.

One thing I will add is that you need to check the water level on any battery that has removeable caps. Even one of these chargers will deplete the water. Deplete it enough and you may have a battery explosion. Take my advice, you don't want to experience this first hand.

Some of the other battery types (I'm thinking of Optimas and the like) may do better with a different type of charger.

JR

Both the Ford original equipment battery and the optima are totally sealed. Not many cars come with the removable caps batteries these days.

The optima is an AGM (Absorbed Glass Matt) type...and I'm not sure about the Ford battery. Battery tender's advertising says it works well with AGM and liquid acid/lead plate batteries. I do know you don't want to charge AGM batteries at more than 14 amps, IIRC....That means Noah's charger should be okay, but I like the lower amp output of the battery tender, as long as I'm not in a hurry.

[javadog]

All my cars, apart from a couple daily drivers, and all of the bikes stay hooked up to a tender 24/7 when not being driven. No issues at all, even the Ducati 916SPS I used to own. If that battery was less than 100% charged, you would not be starting that bike...

I had an Optima in a Lambo. It didn't like to hold a decent charge, so the tender is the only thing that kept it from being a door stop. I seem to have run across a battery charger that used a different way of charging that worked better for the Optimas. I can't recall what it was.

JR