Hal

There is another thread about how long a battery holds full charge. This got me thinking. Our new (to us) '96 is not driven every day. It has an Optima yellow top model D750S in it. The age is unknown. And after long periods, say 4 or 5 days, the car is slow to start. Today, it required a jump. FWIW, I now have a standard charger on it.

One of the posts in the other thread mentioned using a battery tender as routine practice for use such as what we do. Is this normal? Is there a circuit on these cars that draws down the power?

993_Pilot

I can tell you from my experience, that my 993 often sits for 8-10 days while I am out on business trips, and I have never needed one. In fact, (Knock on wood) it always starts right up on the first attempt. My guess is that your battery is getting old and/or weak. On the other hand, for my motorcycles, I use the "Battery Tender Jr." because they often sit for much longer periods. On my street bike, I only use the tender during the winter months, but on my dualsport/dirt bike, the tender is always on when the bike isn't being used because it has one big cylinder and a very small battery with no gear reduction on the starter.

air eater

I've used a battery tender on a 03 M5 that gets driven very little and the battery tested as good as a new unit when I sold it.
I plan to use one on a recently purchased 97 C4S when it arrives.

Bill (NC)

I use the Porsche battery tender as the worst thing you can do to a battery is let it sit for long periods. One thing I found interesting though is it is not for all cars. When plugged into the Porsche you don't even know it's there, but I plugged it into my Tundra once and it lights up most of the instruments on the dash!

endodoc

i have a new optima red top in my 98 993.. it is almost dead after one week . i have put the porsche trickle charger on it and it's ok but i don't think that's the way it should be ....there must be some abnormal electric draw on that thing.. i know it is not related but my my speedster starts after six months with out a charge...

Hal

I agree and hope someone can point us to the source of the problem.

FWIW, I put my yellow top Optima on a charger for the last 3 hours and it started up as strong as I ever remember. I guess a better test will be to see how it does in the morning.

killsbugsfast

Have been using the battery tender religiously for years.
The car alarm consumes enough power that generally after 10 days the battery is too low to start the car.
This type of repeated drawing down of the battery is the worst thing for the battery and considerably shortens battery life.

The quick connect that comes with the battery tender makes it super easy to hook-up on a routine basis.

jimbo3

Do you leave the key in the ignition?

Hal

Only when driving.

Pete Lech

+1

I have them on both cars. Drop 2 extension cords from the garage ceiling.

Slow Guy

Yes I have a battery tender and have used it for about 5 years, however it is only used when the car/bike has not been used for an extended period of 2 - 3 weeks at least.

To answer your question, you should not have to be recharging your battery after only 4 - 5 days, it sounds like your battery is near the end of it's life. Of course you may get 6 - 12 months of use with it like this but why take the chance? Do you wait until your spark plugs don't fire anymore until you replace them?

Edit: ...unless there is something putting a significant drawdown on your battery, in that case get that fixed.

993_Pilot

I agree with this post, and I also wanted to point out that I think the alarm on the MY95 (like mine) is different than the ones from MY96+, so it may consume less power. That could be part of the reason for the different responses. You can also take your batter in to almost any auto parts store, and they will usually test it for free. That will let you know if it is a battery problem or something else. Good luck.

Peter R.

As you can gather from the other thread I've been struggling with this as well. When I first gor the vehicle the battery, which was very old, kept it's charge no probs for a few weeks. With the new battery fitted, it seems to loose the best part of the charge after a week or so, after two weeks it's a non starter. I've been backtracing the stuff I did to the car since the battery replacement, and have discoverd that in fact the ONLY thing that's changed is the fitment of a Kenwood radio/cd player. For the sake of experimentation I will now remove it and see what happens. I'm gonna do a substantial audio upgrade anyway, so I want to get to the root of this.

I am considering fitting a battery switch, but I don't know if the car electronics are up to it. I may fit it in the earth circuit instead of the + circuit to reduce arcing then I throw the switch.

Edit : I've been doing some simple maths on this. If the drain from all sorts of electronics (alarm system, immobilizer, car stereo) is just 0.25 amps (3 watts to you and me), that would mean a 70Ah battery runs dry in just 280 hours, or short of 12 days. That's not even two weeks. I would gather that after a week and a half there's not even enough juice left to start her up.

Peter R.

jimbo3

Switching the battery off means that the computer will have to re-set and the stereo will need a manual re-set each time one switches the battery back on.

Drain from the battery with the car at rest is ~20 to 30 mA, (or, .02 to .03), not 250 mA (.25A) and a 70 AH battery is useless when it's at less than half charge, so multiply your number by ~5 and we come up with about 60 days of life under ideal conditions. In real application, 3-4 weeks is about what one could expect before the battery won't be able to start the car.

The Battery Tender (or similar) is the simple solution.

-Jim

Peter R.

I will measure this tonight and post back.

Peter R.