Ron

I've not driven my car in problably a month maybe a little more I really don't recall. Anyway I thought I'd check the battery voltage since I hadn't had the battery maintainer hooked up. It read 11.54 volts using my Fluke.

I thought I must have killed the battery. To my suprise the car cranked right up no problem. The battery is an 18 month old Optima Red Top. I was suprised that the car could be started with such low voltage.

I'm still concerned about the battery's condition so I took it over to the Interstate Battery store where I bought it and they are charging it up and will then test it.

I've read the previous threads about voltage drain and alternator output and like. I had previously check mine and I think the drain was around 40 milliamps and the alternator output was as I recall about 14 volts.

I'll see what they say about the battery but I wouldn't think it should have drained down that much in only a month or so. Incidently my meter was correct as the one at the battery store read 11.6 volts so my reading was very close

Crimson Nape Racing

I don't think that sounds like you have a problem at all. I would recommend a trickle charger to make sure it will start and to prevent excessive wear on the alternator, but I dare say half the 993's out there would not start after sitting for over a month!

mike cap

Ron,

The 40 ma draw at rest is about right. And bus voltage after about a month of 11.6 vdc is fine. A 12 vdc storage battery when fully charged will only read about 12.2 vdc, and with even a few minutes of load, will drop down to your readings. I agree with Bob, that most 993 owners would only give a 50/50 chance of the car cranking after 30 days or so of sitting idle w/o a maintainer. If my car is going to sit for more than two weeks, I always plug the maintainer in. Don't sweat it. Sounds like you have a healthy electrical system.

David in LA

Rather than a trickle charger, you should use a battery maintainer....either a Battery Tender (I use these on my Ducks) or better yet the Porsche maintainer - a bit pricey but the lighter plug-in makes it convenient.

dale_loch

Ron,
Make another investment in PriorityStart (you already started by getting the red top!). My car sits for long periods of time too and this prevents the battery from ever draining to the point where you can't start the car. Excellent product.
No affiliation, just a satisfied customer.

Dale

Crimson Nape Racing

David is right - the Porsche battery maintainer is the way to go. simply plug it into the lighter socket. That is actually what I have, but trickle charger is just more fun to say than battery maintainer.
Bob

Carrera Mike

Optima batteries should use different kind of charger. Definitely not the ones you use for wet cells. I would think though that for maintenance, trickle(slow) charge should keep it up.

Ron

The red top I have is fully charged at 12.8 volts although I doubt it will go that high now that it's a little older and has been discharged a few times.

According to Optima website it can be charged with a charger (trickle charger) with a voltage output of 13.2 to 13.8 volts at 1 amp maximum current; time indefinate (which I take to mean continuously)

I have a small Guest trickle charger that puts out 13.25 volts at .5 amp so that will work if I religiously plug it in after I drive the car. I made a harness that connects to the battery and then to the charger with a small trailer connector. I just need to use it more.

I think that Priority Start thing Dale suggested is a good idea since it removes the battery from the load at a predetermined voltage, something like 11.8 or 11.9 volts, thereby protecting the battery. Considering the aggravation and inconvenience of a dead battery they are probably well worth the cost.

My questions would be:
1-Can I still use the trickle charger with the Priority Start and if so where do you connect it? I'm not electrically inclined so I do need to be told. I'm thinking the charger wires would stay where they are which is right on the battery terminals.
2-Do you have to make any kind of battery connectors to make the Priority Start unit work?
3-Do you have to cut the cars positive battery cable to use the Priorty Start?

The guy's at the battery shop said they will load test the battery tomorrow to see if it holding its charge.

Ron

Picked up the battery this morning and it took a charge fine. Tested at 12.7 volts (when new it should be 12.8 so no problem there). He loaded tested it and it read 12.5 after the test so it looks like I don't need a new battery.

I think these Optimas can be discharged more deeply, be recharged and be returned to service better than regular batteries. Of course only time will tell.

Ray Calvo

Ron, thinking you should be fine. Recently I snapped the oil tank drain plug so had to order another one. I forgot about the engine compartment light, and left the engine lid up for several days. Well, it completely drained the Optima Red Top battery - stone cold dead. I hooked up my battery charger and left it on the 2 amp setting for several hours; even at this setting the ammeter read over 4 amps. After sever hours, battery hadn't gotten up to 10V. Since it was bedtime, I disconnected the charger and hooked up the battery maintainer. Next day after about 12 hours charging (maintaining?) the battery still hadn't hit 12V. I decided to see if the car would start; it did. I then took it for a 2-3 hour drive, then parked it. The battery had recharged to 12.5V and has held this voltage for a week now.

These Optima batteries are strong (then again, mine is ony a few months old).

I generally leave a digital voltmeter plugged into the cig lighter socket while the car is parked. When (if?) the voltage drops below 12V, on goes the maintainer. I've heard they can be left on continuously, but I don't now because I've got a suspicion doing this was the reason my old battery was dry when it died.

Monique

Had the same problem yesterday.

Got a Porsche battery conditioner (Euros 50) and presto...

Use it on our TT Roadster too.

Ron

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Ray,

Below are the charging instructions form the Optima website for the Red Top.



Recommended Charging Information:

Alternator: 13.8 to 15.0 volts; no amperage limit
Battery Charger: 13.8 to 15.0 volts; 10 amps maximum; 8 hours maximum
Boost Recharge: Maximum voltage: 15.6 volts (regulated).
Maximum current: 60 amps.
Maximum recharge time: 2 hours.
All limits must be strictly adhered to
Float Charge: 13.2 to 13.8 volts; 1 amp maximum current;
Time indefinite (at lower voltage levels).



I am inclined to agree with you that leaving a charger on all the time does not seem to be a good idea. I would think it would dry out a battery too whether it’s lead acid, gel or whatever. The Optima website also says the Red Top is fully charged at 12.8 volts so why would it be good to keep charging it after it reaches that voltage. Does the trickle charger keep the plates in the battery from deteriorating? I don’t know. The Optima is so they say a “High purity lead-tin alloy. Wound cell configuration utilizing proprietary SPIRALCELL TECHNOLOGY” whatever that means.

I’ve order one of those Priority Start units Dale recommended. I like the concept of the unit disconnecting the battery from the load when the voltage gets below about 11.9 volts; it just seems like a good idea. Then if you have not driven your car in a couple of months or so you can always hook it up to a trickle charger if need be. The best price I’ve found on the Priority Start is $59.95 for Battery Mart. http://www.batterymart.com/]

Ray Calvo

Interesting data, Ron. RE battery maintainer, looks like key statement is

"Float Charge: 13.2 to 13.8 volts; 1 amp maximum current;
Time indefinite (at lower voltage levels)."

Would think that this means that continuous use of a maintainer is OK if it meets these voltage/amp requirements.

Gotta think about installation of a Priority Start unit, but thanks for the info.