Battery charging

[Zeke]

Thinking I might be driving tomorrow (don't feel too good right now), I pulled the Carrera out of it's hiding place to find that the battery was once again dead as a door nail. If I don't get in there once every 3 weeks, this will happen. No big deal except that I know each time a battery goes fully uncharged, it's a death knell. This may have been the 3rd time, no more than that.

OK, so I jump the thing and drive it only far enough to get it on a charger. 200 feet. That was 4-5 hours ago at 12 amps on the charger selector switch. I'm seeing the meter go down, but not too darn fast. It started out at 6 amps and is now just seeing 4. Is this an indication that my Interstate is about to give up?

If so, I'll go get an Optima when I can. I sure don't want to play the alternator game right now.

Oh, er, I just went out to see the date on the battery. I think I just answered my own question. 4/02 = senior citizen. Well, scheet.

[Formerly Steve Wilkinson]

Master switches are a cinch to install. If I know I'm not going to driving my car for the next five days or more, I just pop the hood and turn off the master.

[Newsboy]

Hopefully, you are disconnecting the battery from the car before charging. Get a good multimeter, (around $20.00). A new /good battery tests around 12.8, 12.4 is around 40%. Usually won't start much below 12. You could also use an automatic .5 amp trickle charger to maintain the battery. Also, Sears will test your battery & let you know if it's time to replace.

[dlague]

Sears!!!! they may just sell you a $150 battery and break the case while they are installing it like they did to me on a trip! Good Work!

[Zeke]

I have multimeters and a load tester. I guess the question is how long does a normal battery take to charge fully from dead? I think that would be good info to know.

Meanwhile, I'm going to get a new battery. 8 YO is old enough.

I don't think it makes any difference if the battery stays hooked up in the car. My other car that is never driven stays on a maintainer with the battery installed. Show me how that's wrong.

[PCA7GGR]

Costco has Optimas.

[ischmitz]

Milt,

A "normal" starter battery has between 50 and 150 Ah of capacity depending on its size. This means at 10 Amperes it would take between 5 and 15 hours to fully charge it. Just multiply the current with the time. My guess is that the stock Porsche battery in a Carrera is about 75 Ah.

In the U.S. the capacity doesn't seem to be stated. Instead you find the cold-cranking Amps. This is merely a fancy marketing move stating how low the internal resistance of the battery is.

And you are right, every time you deep-cycle a battery irreversable sulfation processes occur and reduce its storrage capacity. The net effect is that the charging current rapidly falls indicating that the battery doesn't take more charge. Your charger assumes that the battery is full but doesn't "know" about its reduced capacity.

And BTW, get a Yellow-top Optima if you encounter deep-cycling. I killed one Red-top by deep-cycling it. Else a good battery maintainer can prevent issues.

Ingo

[Zeke]

Thanks, Ingo. So it's not a bad thing that the battery wants some time. I don't like to leave things unattended, so I unhooked the charger last night before bed. I'm going to resume charging this morning.

Happy Thanksgiving.

[rick-l]

If the amps are tapering slower than you remember you may be in trouble.

Here is some info on what happens to a discharged battery

sulfation

[911pcars]

Milt,
Heat is a killer of batteries. Thus, don't use a high charge rate to recharge it. Use the trickle charger as long as you can to bring it up to speed. If it doesn't respond after 24 hours, it may be time for a replacement. Some Optimas require a special charging technique.

The cold cranking amp spec (CCA) is a reliable method to compare batteries, not just a fancy marketing scheme. Many manufacturers use other, less known numbers to avoid direct comparisons with batteries using CCA numbers. Typically, there's a direct correlation between weight and capacity. A lightweight, 15 lb. battery, for example, might be fine for moderate climates. However, its low capacity will shrink even more (like all batteries do) once the temps. drop.

I agree. Keep the battery on a maintainer during periods of disuse and/or disconnect it from the system. Have a good ride (well, you're probably on it now) and keep the shiny side facing upwards, the one-of-a-kind nose too.

Then, it's turkey time.

BTW, As a battery nears full charge, the EMF (electromotive force) of the battery increases and the charge rate decreases. This is normal. If the charge rate doesn't change, this tells me the battery isn't accepting a charge.

Sherwood

[Joe Bob]

I run a yellow top marine Optima in my cab......I tend to park it for a couple of weeks when the weather gets bad or I just feel the need to keep from killing myself in it.

It's gone flat numerous times but still takes a charge after five years.....

[pwd72s]

Milt, if you do go optima, keep in mind that a low amp charge is best for these. Beyond a certain level, you'll fry an optima. Don't have my paperwork handy, but IIRC it's 14 amps? I just use a battery tender on the optima in my Power Wagon. It's a slow charge, 1.5 amps or so? (Can't remember the exact figure) Has a cute little light system...red if charging, red combined with flashing green if 80% or more charged, and solid green when charged. I just kept my Porsche plugged into one full time, since the battery tender has an auto off & on feature.

[davidbir]

I agree on the Battery Tender (capitalised-it's a brand name). You should be able to pick one up for about $35 and they really keep the battery up to specs-no good if the battery is dead flat though.

As regards charging at a low level: Until recently I was a sailboat owner and had a bank of six batteries to keep charged. The standard procedure on boats is to use a BIG charger-40 to 50 amps with a computerised control system. This is said to reduce sulphation. I suggest reading Nigel Calder's "Boatowner's Mechanical and Electrical Manual" for real in depth info. I am absolutely no expert!
I was however, Service Manager for VW/Audi/Porsche for a few years and saw some mechanics get seriously hurt when disconnecting battery chargers incorrectly-they only did it once! ALWAYS unplug the charger before connecting or disconnecting it to the battery!

[Formerly Steve Wilkinson]

"I don't think it makes any difference if the battery stays hooked up in the car. My other car that is never driven stays on a maintainer with the battery installed. Show me how that's wrong."

Not talking about a battery on a maintainer. I'd need a 200-foot extension cord to keep my car on a maintainer in any case. All I know is that if I leave the battery hooked up, it'll go dead in a month. If I turn off the master switch in November, it'll start the car just fine in April. So for me, at least, it matters if the battery stays hooked up in the car.

[Zeke]

"Not talking about a battery on a maintainer"

Neither was I. I was referring to newsboy's comment. I too have no electricity where the car hides.

[Newsboy]

Just to clarify. I keep .5 amp battery maintainer with automatic on/off hooked up to my car in winter, when I only drive it 3 or 4 times a month. I was talking about disconnecting the battery, if you are going to use a regular battery charger to bring it up quickly. I have read that there is a chance you can do some damage to the electronics. Perhaps someone with more expertise, can address this?

[Rob B]

It shouldn't be going dead!! Either the battery is failing or more likely, there is a drain(short) in your car. Disconnect the neg. cable and connect your volt or amp meter in series(one lead to your battery terminal, one to the cable) If the meter reads a full 12 volts or the amps drain is more than a fraction of an amp, you have a short and buying a new battery won't help.
To find the drain, pull fuses and disconnect wiring harness plugs until you find which circuit causes the meter to return to zero or at least fall significantly. This may take a while or you may be lucky. Let us know, Rob

[ischmitz]

Some heavy duty chargers have a high-setting. If your battery is not holding much charge and its internal resistance gets high these chargers can raise the system voltage beyond 15 or 16 volts and that can harm electronics. So it is a good idea to take the negative off before hooking one of these up to the car.

The trickle and maintaining chargers operate with much lower currents and won't do any harm to the car. You do not need to disconnect the battery while it is hooked up to one of those.

And modern cars do drain the battery slowly. Alarms, clocks and the like do consume power and can drain a battery within a couple of month. And if you have any aftermarket equipment (stereo, etc) that gets permanent power this accelerates the effect. In addition a leaking diode in an old alternator can also drain the battery.

[RWebb]

Originally Posted by Formerly Steve Wilkinson

... I'd need a 200-foot extension cord to keep my car on a maintainer in any case. All I know is that if I leave the battery hooked up, it'll go dead in a month. ....

solar cell maintainer - in mail order catalogs

[dependencies]

Originally Posted by Formerly Steve Wilkinson

Master switches are a cinch to install. If I know I'm not going to driving my car for the next five days or more, I just pop the hood and turn off the master.

will someone tell me how to fit one of these, and where to interrupt the juice

under bonnet, or behind dash?