Battery drain and thoughts on alternators.

[ray_hennig]

Hello All,

I'm guessing a bit here, but here's the problem:

A couple of years ago, my local MB dealers were doing deals in batteries so I got one. I knew it might be physically too big but it was the electrical capacity that convinced me.

Anyway, my reasoning was that as the car spends all its time in the open, a huge battery would stay charged for longer and delay any flat battery misery.

In this I thought I was being very clever, just as I thought I was in butchering the battery tray and very firmly securing this vast battery.

The good news is that the battery fits very well and is 100% stable.

The bad news is that I've never had the car drain its battery before when only being left for about 2 weeks. This "hang the expense" battery is the worst on record.

I recently read on one of the other boards someone who said something like, "... we need bigger alternators because of the high capacity batteries that are being installed these days". Or words to that effect.

Is there any truth in this?

Would I be better off going back to the old style, lower capacity battery?

Should I fit a higher capacity alternator?

Or, perhaps, I have something draining the battery? My tests have shown not.

Incidentally, the car starts absolutely instantly when jump leads are connected, even of from an ancient Renault 5.

Any comments on this, anyone?

The best to all.

RayH

 

[RBYCC]

Ray

It's not the physical case size of the battery but the amp hour rating.
The higher the amp hour rating the longer it takes to discharge.
The other rating you'll see on a battery is CCA or "cold cranking amps".
Again the higher the number the better.

The output of the alternator depends on your load with the engine running.
You want to make sure that engine running you see 12.5-13V + at the battery.
Weak voltage regulator in the alternator can prevent the battery from fully charging.

If you are having this problem with a 124, then more then likely it's the constant drain from the Becker security module under the carpet in the passenger footwell (USA LHD location ) sedan and coupe and behind the left trunk panel cabriolet.

Just unplug the two black cables from the Becker unit and you'll remove a constant battery drain.

On the 94-95 there is an immobilizer relay behind the instrument cluster that also has to be jumpered out.

Ed A.

 

[ray_hennig]

If you are having this problem with a 124, then more then likely it's the constant drain from the Becker security module under the carpet in the passenger footwell (USA LHD location ) sedan and coupe and behind the left trunk panel cabriolet.

Just unplug the two black cables from the Becker unit and you'll remove a constant battery drain.

On the 94-95 there is an immobilizer relay behind the instrument cluster that also has to be jumpered out.

Ed A.

Thanks for your reply.

The problem was never there before installation of the massive battery.

I have measured current drain and can detect nothing unreasonable.

The basic question is "What has changed?"

I'm a bit in the dark so maybe I should start researching battery parameters, as you suggest.

Thanks again.

R

 

[RBYCC]

Thanks for your reply.

The problem was never there before installation of the massive battery.

I have measured current drain and can detect nothing unreasonable.

The basic question is "What has changed?"

I'm a bit in the dark so maybe I should start researching battery parameters, as you suggest.

Thanks again.

R

Ray

Look at your charging system by reading voltage with the engine running at the battery terminals...
Larger amp hour rated battery will take longer to fully charge.

Ed A.

 

[brucemillar]

You may have purchased a duffer.


Find an Indie that has a battery load tester or drop tester. Takes five minutes to test but could save you stress and money.

 

[Ted]

First of all

INSTALLING A LARGER CAPACITY BATTERY WILL NOT AFFECT YOUR STARTING.

There. I said it.
As has been said, you will have more capacity, so it will take longer to discharge. It will also take longer to fully charge, but no longer than to charge it to the same level as the smaller battery.
Bigger capacity batteries also usually come with more CCA. A good thing.
If your battery isn't starting the car it can be a number of things.
Is the battery flat? Check at a reputable auto electrician or use a hydrometer. If it is flat/low charge then this will be either a charging problem or a permanent drain.
If the battery is fully charged then get it tested to see if it is able to hold the load during a high rate discharge test (fun). if it can't hold the load it is faulty. If it can hold the load you have a problem in your starting circuit.

So get the battery checked out and make your further diagnosis from there.

One thing I haven't mentioned is overcharging, but I am sure you would know about this as the battery would require constant topping up and would stink.

 

[balge]

Is this battery so big a terminal is touching the bonnet...?

 

[Ted]

Is this battery so big a terminal is touching the bonnet...?

You would know if it was

 

[balge]

You would know if it was

Heh, if would go flat in less than a fortnight if both the terminals were touching...!

Just wondering if it could be contacting intermittently though, had a Triumph that used to do similar, no problem with the battery lid off testing it, soon as it was buttoned up it used to bounce around inside the cover and start shorting...

 

[Rory]

Larger amp hour rated battery will take longer to fully charge.

I wonder if there's something in this - years ago my wife had a little car which came (used) with an immense battery. She only used the car locally and it was often flat. I swapped it over with the tiny battery from my company car, and neither had any further difficulty. I put it down to the small amount of charging the big battery was getting being somehow 'lost' in the battery.

 

[ray_hennig]

Heh, if would go flat in less than a fortnight if both the terminals were touching...!

Just wondering if it could be contacting intermittently though, had a Triumph that used to do similar, no problem with the battery lid off testing it, soon as it was buttoned up it used to bounce around inside the cover and start shorting...

This is not my problem as the 'immense' battery is only longer than the original; not higher or wider. It's solidly mounted with the positive terminal in exactly the same place as with the original MB battery.

Thanks for your response.

RayH

 

[ray_hennig]

I wonder if there's something in this - years ago my wife had a little car which came (used) with an immense battery. She only used the car locally and it was often flat. I swapped it over with the tiny battery from my company car, and neither had any further difficulty. I put it down to the small amount of charging the big battery was getting being somehow 'lost' in the battery.

My immense battery has had the opportunity to charge up over 1000 KMs and it still discharges in less than 3 weeks.

The local garage that tested it said it's fine and such things are normal.

Huh!

There's a French (I live in France) expression, "C'est comme ça." Sort of, "That's the way it is."

The expression is often used when people don't know the answer!

R

 

[RBYCC]

My immense battery has had the opportunity to charge up over 1000 KMs and it still discharges in less than 3 weeks.

The local garage that tested it said it's fine and such things are normal.

Huh!

There's a French (I live in France) expression, "C'est comme ça." Sort of, "That's the way it is."

The expression is often used when people don't know the answer!

R

The only constant drain on the 124 battery is the Becker security module.
I've owned my C124 since new in May 1988 and disconnected the Becker alarm module years ago to lessen battery going dead when the car sits for a time.
I still use a battery tender when the car will sit idle for over a week.

Check the drain on these fuses at the rear of the fuse box..

 

[SL350_SWINDON]

aldi charger is very good.