DBJoe996

Background - 99 C2 126,500 miles. Replaced battery in Sept. 2009 with Sears Die Hard Group 48 due to sluggish starting and sometimes no start condition. That helped, but finally had to replace the starter as well in Dec. 2010. All has been well since then, until -
Symptoms - Use the car as a daily driver and sometimes make 5-6 stops a day. It gets some highway miles to West Palm Beach and St. Augustine every so often, and lately to Tampa due to wife's mom in hospital. The heat in Florida has been oppressive lately, 90+ daily (last night at 5:30 it was 98 on the back porch!). Of course that means the AC is running constantly as well as the cooling fans and even the engine compartment fan. Temps were running on the high side of 180 and I knew the car was having a time of it with the heat and starts and stops. Finally today, two no starts after some runs. Seems the car has been sluggish again lately and the starter dragging on re-starts. Conclusion - Time for a new battery!
Fix - got it started and drove home to do some research on replacement battery. Wanted an Optima like I put in the wife's Mini Cooper, but saw that that was going to require some work on the bolt down, so, instead opted to run to Sears after looking at the Diehard AGMG Group 48 replacement batteries. No warranty on the old battery but didn't care. Bought the new AGMG Group 48 battery, installed in parking lot, perfect fit, car started like it was brand new! Didn't realize how sluggish the starting had become. Battery - Diehard AGMG GP48 Item #22850748 for $174.99. I swear the car seems to run better and the fans must have been running slower (meaning the temp was higher) because now it is 90 degrees and the temp is right where it belongs between the 8 and the 0. A good day and smiles and miles to go!

Imo000

The fans should not be effected by the battery. The battery is only there to start the engienand to act as a buffer for the charging system. Your battery could be low because the alternator is on it's way out. Would have been a good ideanto load test the old battery. What shape is your alternator?

DBJoe996

They did load test the old battery and said it was fine. Replaced anyway due to age and reliability. Alternator output at ~13.7 volts. I did notice while driving that the gauge reading was low, ~12+ volts while running and under the conditions stated. With new battery it is back up to the middle, a tad north of ~13V. Starts like a champ! I understand your comment regarding the fans, but I do think that the low voltage/amps available from the battery under high load conditions was causing an overall low voltage condition. Car batteries are a disposable item to me, like tires and belts. I am sharing mainly for the benefit of fellow members who may be looking for a perfect fit battery replacement at a reasonable cost. Thanks!

Imo000

Lets wait a few weeks before declaring victory. I still think your alternator is marginal. It will take a little time to slowly drain the new battery.

Divot

I just changed my battery today. First, passenger window acts weird - Hit up button and it climbs to the top, then reverses about 1/4 way down. Only way to close is to hold the button. Close door with closed window and same 1/4 way down reverse. PITA. Then a couple of slow starts, then won't turn over. New battery fixed it all.

It's been over 100 degrees every day for a few months now. Batteries hate heat, and Porsches hate weak batteries and do weird things.

Imo000

Actually, batteries hate cold. You ron't have to beleiv me, just google it. Also, 100F souldn't be an issue. Most engine compartments get hotter than that and that's where most batteries live.

Divot

Link with nifty chart

And it's been up to 115, not just a wimpy 100.

thstone

The ECU will detect low battery voltage at startup and try to compensate for the possible lack of a strong spark. A new battery will actually make the car run better!

Imo000

That article is on battery storage over 6 mths, not relevant in this case. When you'll be around engines long enough, you'll see. 115F is nothing when it comes to engine bay temperatures. Most car have thermostats that are above 160F. Imagine how high the temperature goes when it gets heat soaked after shut down.

Divot

How is it not relevant? We are talking battery life, not cold cranking amps. Please return the courtesy and provide a link showing that hot temps increase battery life, as I'm always willing to learn.

And I don't know how old you think I am, but I'm already well past AARP age.

Imo000

Your link is storing batteries for extended periods of time and I didn't say anything about your age. If you would been around engines long enough (not relevant to your actual age) you would understand what cold does tona battery. Unless you boil a battery by a faulty alternator (been there 3 years ago) 115F has zero effect on a good battery. Up here everyone know what happens to a battery when it gets really cold. I don't mind having an intelligent conversation but I won't get into a pi$$ing match. Not something as basic as batteries.

KNS

Heat kills batteries too, ask anyone who's lived in Arizona for a while.

Imo000

Ok.

Divot

I have reread all of my posts and I believe I have been courteous. I'm not in any sort of contest, I'm just politely asking for you to provide a link showing that hotter temps increase battery life, stored or in use. I would like to learn more, especially if my understanding of the effects of temperature on amps (cold=bad) and battery life (cold=good) are wrong. I didn't start "if you had been around engines long enough", or "up here everyone knows..." I'm just asking for a link, as I provided you, rather than basically just being told I'm a naive dullard.

If it encourages you to provide the link, I started working on my Chevys, including a Corvette, in the 70s. A 914 and 911 in the 80s. I lived in Michigan and in the snow belt, and know cold weather and what happens to batteries. I have spent exactly one winter when the temp didn't drop below zero.

Imo000

I never said hotter temperatures increase battery life, those are your words. What I'm saying is, unless you boil a battery or I suppose not maintain it and it dries out, 115F is not a high temperature to kill it. As I said before, most batteries live in the engine compartment where it get a heck of a lot warmer than 115F. In the 996, the battery is outside of the engine compartment therefore, it has a very comfortable environment. In Phoenix the lack of maintenance what kills it not the heat.