BLK993FL

First, thanks for a great forum especially for a new Porsche owner.

Just wanted to post my recent battery experience since I have learned much from other similar posts. My new to me 96 993 C2 came with Optima RedTop. Battery date March 2010. In 2007 same battery was installed Optima Red 75/35. So two of those batteries in 5 years. The car does sit between drives, every few weeks. I have a CTEK Charge O Mat with cig lighter adaptor that I thought was working? After about a 4 week sit with ctek on, nothing but clicking noise when trying to start. After determining the battery was dead, I now have an Interstate MTP-91.

CTEK manual says for lead acid batteries. It seems like other are using the charge o mat for AGM type batteries versus lead acid. Does anyone know for sure if the charge o mat will actually maintain an AGM battery, especially since manual only reference lead acid???

Thanks for posts on batteries, clicking noise when trying to start, etc. Extremely helpful...

IXLR8

Depending how they were charged, that will happen.

Do you place the battery on a charger/maintainer during the hot summer months as well? If so, what are the temperatures while doing so.

Optima is extremely vague when publishing "recommended charging information"...like 13.3 to 15 V. They've told me that it doesn't make a difference, which I find impossible to believe when the life of the battery is concerned. Yet, they also state that "all charge recommendations assume an average room temperature of 77°F (25°C)". So what happens at 100°F? Chances are that same charge voltage overcharges the battery and you should never ever overcharge any VRLA battery.

BTW, batteries will last very long if they are charged properly by the vehicle charging system or during off-season maintenance. The one in my daily driver is in its 13th year and on another car I had, it lasted 16+ years.

I'm looking forward to testing Optima's new charger in my lab. That should be interesting. I'll post those so-called proprietary voltage levels.

mike cap

BLK,

If you spend the time here researching the Optima batteries you'll find that the general opinion is that they are not a good choice for a car that sits for long periods of time.

Your Interstate is a good choice. I use the Diehard International (looks identical to yours - probably the same manufacturer) and have replaced it once in ten years. And then I probably didn't have to do that.

I use the Porsche Battery Maintainer when the car is sitting for more than a few days or in winter storage. It is probably a similar unit to your charger.

You made the right choice to go back to a traditional battery and should be in good shape for a long time.

97_993C2

I have a CTEK Multius 3300, not a Charge O Mat, that has a specific setting for charging AGM batteries, and an Optima Red Top that is going on 4+ years.

I think the general consensus is Optima batteries are fine if they do not get overly discharged, which means a battery maintainer, designed with AGMs in mind, when sitting for long periods. Over discharging seems to have a dramatic impact on AGM battery life as the OP has seen.

I like AGMs because I don't have to worry about battery acid leaks/overflows eating holes in my trunk carpet. Ask me how I know.

Slow Guy

I have an Interstate in mine, no issues.

Side note, If FL has a emissions/OBDII test save yourself some (potential) hassle and wait until you after you get it tested before you disconnect the battery.

Personally I don't have a problem with mine but others aren't so lucky. (Look up "OBDII Readiness indicators")