dryadsdad

We have a '95 993. The battery is clearly far enough down in capacity that it demands replacement. I have read in Excellence that some late models are very sensitive about battery replacement and will go into limp home mode if the battery is disconnected or run to flat. I sure don't need that.

I would guess this doesn't apply to the 95's but I'd like confirmation before we pull the current battery. Also are there any gotchas in this operation? That is, does the 993 do poorly with some sorts of replacement batteries such as AGM's, etc? Thanks.

mike cap

Easy replacement job, like any modern vehicle. The hard part is getting to the darn battery. If you have a battery maintainer you can leave it plugged in to save all you codes and such.

Go to Sears and buy the Diehard International Group 48 # 22833348. Drop in fit with the vent set up the same as the OEM battery. It's the only battery I've used in ten years of ownership. No issues at all.

dryadsdad

Thanks Mike. We'll do exactly that and yes, we have several Battery Tenders (we also ride bikes) so we'll run that in parallel to keep the settings.

mike cap

You're welcome. The part number for the Sears Diehard is from my records a couple of years ago the last time I replaced my battery. Their part number ID may have changed, but the description I gave will get you the right battery.

One thing I did do is relocate the battery vent from the LH fender to the floorpan. I was never happy with the thought of a bad battery spewing acid in to the fender well. I just removed the closest floorpan drain under the spare tire and installed a grommet and the fitting from the fender. I think the only thing I had to source was a longer plastic vent line. Now if the battery overcharges it will vent under the car.

dryadsdad

I'll be sure to make the vent able to vent. AFAIK, Sears doesn't change its call numbers so that should be good. The group number is surely the same.

911Dave

I suggest you save yourself all that hassle and buy a sealed AGM battery. The Optima Red Top is a great choice.

mike cap

Ok, good luck. Easy DIY.

I'm off this topic with no interest in a discussion of the AGM and Red Top debate. About 99% of the battery topics I've read here for the last ten years concerns these batteries unsuitability for a typical 993.

dryadsdad

Why would an AGM be unsuitable for a 993? I don't get it.

IXLR8

For starters, the charge voltage of our 993s is set a bit on the low side. The voltage across my battery while driving is 14.2V at best with it being between 14.0V and 14.1V most of the time. Some AGMs require higher voltages. Another disadvantage to an AGM is that they cannot be user maintained.

Mike mentioned plugging in a battery into the cigarette lighter to maintain codes, etc. Don't forget to wrap something around the positive battery cable terminal so that it does not short to ground when you are disconnecting the old battery.

An aftermarket battery that is 100% identical (other than case color) to the Porsche battery is an East Penn 648 MF battery.

dryadsdad

I thought one advantage of the AGM was that there is no maintenance possible. Over in BMW bike land, there was some sort of fuss about using AGM's with some chargers. That is, some chargers didn't seem to work with them. Perhaps this is due to the voltage issue.

The 648 doesn't seem to be sealed.

Thanks for the tip on the positive cable.

Jack of Hearts

I've had three Die Hards in my 1996 in eight years. I found that they did very poorly if I went more than a week without driving the car--every one of them ended up with a dead cell within two years. I switched last year to the Porsche Kamina Moll---have not had any further problems.

and, FWIW, I just disconnected the terminals and put in the new battery like it was a regular car. It never had any effect on the OBD that I could see--no codes, no warning lights, no nothing. You do have to reset the radio code after doing this.

dryadsdad

Radio code the least of my concerns. Thanks.

IXLR8

Consumers usually buy into the advertized advantages of AGM batteries that do not really have a real world use to us.

Primarily, those advantages are:
1) very low rates of self discharge.
2) very high cold cranking amps (CCA) due to their very low internal resistance.

On 1) above, thats true but who cares. Our AGM batteries aren't stored on a shelf where their low rates of self discharge occur...they are in a car that has a standby drain current of roughly 30 mA. So there is one feature that is totally unimportant to us. It would be to a vendor who has a couple hundred AGM batteries sitting on a shelf.

On 2) above, how many 993s are being started at 0F...not too many. And if you need those CCA, why not make sure your battery and starter terminals are corrosion-free, zero resistance points, first.

They are not sealed as so many believe. Yes, AGMs and GELs fall into the SLA (sealed lead acid) battery class, but only because you cannot top them up. They are vented in case of over-charging.

IXLR8

It isn't and neither was the OEM Porsche battery. Thats why we have a vent tube; not just for leaks, but for safety reasons. No battery that cannot be vented to the exterior should be used in an enclosed area. So if it doesn't have a spigot to connect a vent tube to, pass on it.

I chose a FLA (flooded lead acid) battery over the AGM that East Penn also sells for roughly $100 more. Its the 9AGM48.

I highly doubt I could have seen 16 years out of an AGM battery which is what I got out of the OEM FLA battery before the car was sold. The FLA battery in my present daily driver is now in its 13th year and going strong. The charging systems in both vehicles are spot on.

dryadsdad

Good info. Thanks. I tend toward AGM in bikes but never really looked into the why of it. I just followed the crowd when these became available.