flat battery question

[wben]

I left the ignition on in my truck & the battery is completley flat. I have a trickle charger that needs at least 3Volts in the battery to enable it to start charging for some reason. I normally just jump start the ute with another battery and then hook up the charger after.

I am wondering if i can hook the battery charger up then give it a boost from a cordless drill battery & some aligator clips to start the charger working? This would save me having to take a battery out of another car. Not sure if its going to work or fry my drill battery?

 

[NitroPress]

If the battery you ran flat is more than about a year old, you've probably killed it - you might be able to get it to take a charge, but it will never be reliable again. At least, that's been my experience. I've nursed failing batteries along when I had to, but once a batt with some service time on it has a deep discharge, it's ruined and becomes an unreliable PITA.

If you need the truck to start and run reliably and the $75 or so for a battery won't kill ya, just replace it.

 

[wben]

Nah mate its less than a year old. i have a bad habbit of leaving the acc. switch on. its not a daily driver and if i jump start it works like new again. I can leave it sit for 3-4 months then start it no worries. Its a top end bosch brand one i bought it for that exact reason. I should just leave the trickle charger on all the time i know!!

 

[justsam]

I see nothing wrong with using your drill battery to "fool" your charger so it will then charge your car battery, as long as the drill battery is somewhere near 12 volts. Make sure the car battery remains charging once you take the drill battery away.

I tend to keep small trickle chargers on cars and motorcycles that don't see regular use, and there are "intelligent" chargers that are pretty reasonable in cost now.

 

[HOTFR8]

Make sure you use a charger that does not overcharge the battery as posted above an inteligent charger or tender type charger. You usualy have to jump start the vehicle from another vehicle before they will charge. How about leaving yourself a note on the dash do not leave the key in accessory position that way you may not have problems.

 

[Squankum]

How about leaving yourself a note on the dash do not leave the key in accessory position that way you may not have problems.

Maybe, but I think the feller needs a large solar panel on the roof!

 

[wben]

Tried it with a 14v drill battery. Jumped out the terminals and instantly the charging light turned on!! Thanks for your responses guys. This sure beats removing a battery from another car!!

 

[Drew_flux]

Ive had to use a "jumper" battery to get things charged on my durst charger. what i do now if the charger will on start. i put the battery on one my diy dirty chargers. one is just a wall wort transformer with clips on the end of the cable (slow charge) the other is a downlight transformer (med charge 5amps).

 

[RobSmith]

I am wondering if i can hook the battery charger up then give it a boost from a cordless drill battery & some aligator clips to start the charger working? This would save me having to take a battery out of another car. Not sure if its going to work or fry my drill battery?
Yep, I reckon that will work...I've done it with lots of battery drill batteries and they accept the new charge so I don't see what can go wrong with a car battery...If it's dead it's dead ! Give it a go. It won't hurt a dead battery.

 

[Milton Shaw]

You could probably use a 9 volt battery. Should work to fool the charger. They use a 9 volt in the socket for the lighter to keep the computer codes alive, so it should be enough to fool the charger. It's polarity is marked unlike a drill battery so you shouldn't get it reversed.

 

[HOTFR8]

Maybe, but I think the feller needs a large solar panel on the roof!

I must have missed something about Solar panels

Tried it with a 14v drill battery. Jumped out the terminals and instantly the charging light turned on!! Thanks for your responses guys. This sure beats removing a battery from another car!!

Why do you have to remove a battery from another car just to Jump start you car with battery problems ? I would think it better to have a car running to jump start another car. Unless you have one of those Jump start battery packs.

You could probably use a 9 volt battery. Should work to fool the charger. They use a 9 volt in the socket for the lighter to keep the computer codes alive, so it should be enough to fool the charger. It's polarity is marked unlike a drill battery so you shouldn't get it reversed.

I would not do this a the 9 volt battery could explode. All they are designed to do is keep enough power in computers etc. so they do not lose memory settings.

 

[wben]

i have to remove the battery because the car is in the shed and there is not enough room for another car

 

[Zeke]

I would not do this a the 9 volt battery could explode. All they are designed to do is keep enough power in computers etc. so they do not lose memory settings.

And that's all they do when you plug them in to keep the computer memory alive. Usually the main battery is getting disconnected at this point so there will be no backfeed of 12v for any period of time.

I use a motorcycle battery but only because I have one handy.

 

[Alchymist]

And that's all they do when you plug them in to keep the computer memory alive. Usually the main battery is getting disconnected at this point so there will be no backfeed of 12v for any period of time.

I use a motorcycle battery but only because I have one handy.

I'm suspecting a 9 volt battery designed to keep alive the computer memory most likely has a diode in series to protect it - then the 12 volt battery will not damage it. Typical battery backup circuit in many electronic devices.

 

[Daniel Dudley]

Did you try just hooking up the charger and walking away for a few hours ? Mine will eventually start charging if I hook it up.

 

[Zeke]

^^^^^^^^^^^^^^
Congrats on 1000 posts!

 

[ket-tek]

What I've done in the past is to hook a set of jumper cables to parallel the bad battery to a good battery and hook the charger up to the good battery as well. Charge them together for an hour or two, and then disconnect the good battery and put the charger on the bad battery to then complete a full charge.

I've had this technique bring back some batteries that would otherwise not charge on various types of chargers nor off the alternator after being jump started.

 

[rsa]

What I've done in the past is to hook a set of jumper cables to parallel the bad battery to a good battery and hook the charger up to the good battery as well.

Optima's recommendation is to hook up the charger to the deeply-discharged battery. In the picture below, the Optima is the deeply discharged battery.

 

[HOTFR8]

i have to remove the battery because the car is in the shed and there is not enough room for another car

How about a longer set of jumper leads ? Many road side sevices use them now as they pull up behind when you when the vehicle is in a position they can not reach the front such as in a garage or angle parked to the curb. I made up a heavy duty set of jumper leads just for this purpose and they work well.

Optima's recommendation is to hook up the charger to the deeply-discharged battery. In the picture below, the Optima is the deeply discharged battery.

You will find all tender chargers on the market will recomend the same thing to charge a dead flat battery. Tricks them into charging the flat battery.