Battery charger help needed.

I have one of these modern electronically controlled battery charger, it works fine when there is some charge left in the battery, but it won't attempt to charge a dead battery as the battery full light comes on.

I have heard somewhere that if you connect a completely dead battery in parallel with a partially discharged battery, this will fool the electronics in the charger and charging will commence as normal! I have a dead battery in an O/t car that I need to charge so I can move the car and a partially discharged battery in my truck that needs charging.

Normally I would simply swap batteries asnd get on with it, but as both batteries have different post designs this isn't feasable, I don't have a booster pack that works so I'm going to try the above. Otherwise I will have to jump start the car from another vehicle. I'm reluctant to buy a new battery as I intend to keep the car inside until next spring.

 

You probably have already solved, I'm presuming that you are charging an AGM battery and that your new charger has a switch position for AGM's. Anyway the parallel battery hookup as you noted will work for AGM's even w/ and old style charger. More info out there http://www.hotrod.com/techarticles/general/hrdp_1009_how_to_charge_a_agm_battery/viewall.html

 

Quite true, and this trick works well.

 

I didn't know that, but wish I had, when I got so disgusted with the charger I used in our camper that wouldn't re-charge the battery, that I smashed it to pieces. It made me feel better, I must admit...

Brian

 

I tried it anyway, and it worked ! Thanks guys.

 

I remember now where I picked up this tip, it was for re charging a totally dead jump start park, that would not charge via it's own transformer, connecting in parallel to a semi charged battery on a normal charger has worked for me a couple of times but like most things these must also have a limited life, mine was a cheap one and a few years old.

 

how big does the second battery have to be?

 

Doesn't have to be Big at all, just another 12v car battery that has a decent charge to it.

 

so the idea is to complete a circuit and when the fancy charger sees a complete circuit it will start to charge?

 

Most small tender style chargers will not charge a dead flat battery. Once tricked by the jump start method they can bring an old battery back to life.

 

I believe the problem is there is some circuitry in the tender type chargers that doesn't let them charge if the battery is completely dead (or close to it) By putting another battery in parallel, it thinks the battery is just low and the charging commences.

 

I am not sure about the new electronic chargers,but we had an old Exide charger at the shop for many years,we had a AA flashlight battery taped to the handle,a quick touch of the neg and pos clamps to the battery would kick on the charger,and it could be put on the dead battery that needed charged.

 

That's wild! (I thought I was slick using a 9 volt for the same purpose!)

I am guessing that just a 1.5 volt surge will trigger the charger? Good to know.

Someone please rate this thread with 5 stars! It will help everyone, eventually.

 

How do you hook the two batteries exactly? I don't understand that witchcraft called electricity.

 

You hook all batteries/charger in parallel, + to +, negative to negative.

The premis is that the charger or trickle charger thinks a dead battery is a dead short & won't charge it. The partially charged battery fools the protective circuit and turns on the charger. I've had to do this a couple of times on my Optima battery in Faye.

 

So + charger to + good batt. then + to dead batt.?

 

(charger) (battery 1) (battery 2)

+ ______________+____________+


- ______________-_____________-

Shows 2 batteries in parallel being charged. Some wiring diagram lol.

 

I've done this trick many times, even the battery on my riding lawnmower is enough to do the trick.

 

Got it. Thanks.

 

We used to do this at a shop i worked at:

Take an old working headlight and solder a couple of wires with aligator clips on to the terminals.
If a battery wont take a charge just hook up the headlight. The charger senses the draw and starts charging.

This also works with a battery still in the vehicle. Just turn the headlights on...

I have extended the life in quite a few batteries that other people would have replaced.

 

Very cool tip^^^.....

 

That is correct. Just be aware some Conventional chargers will also over charge a battery. This is the difference between a Tender style charger and a Conventional battery charger.

Do it the same as you would to jump start a vehicle then add the tender charger to the dead flat battery after a short time you can disconnect the good battery.