the battery of my 996 C2 has been connected to Battery Tender Jr. for almost 2 days and the tender indicator never turned green which means the battery never been fully charged,,

do i need a new battery?
if yes, what specs should i seek in an aftermarket replacement battery?
do i have to have a vented battery?

 

How old is the battery?

I can drive for over 300 miles. Park the car. Plug in the Porsche Battery Maintainer, and the light won't go "green" for 1-2 days. Seen it take up to 4 days after the car was off the maintainer for about 1 month. I consider this normal. May be for you too.

 

the battery is 3 years old,,

 

That's not too old. One of mine is OEM on a 2006 987S. I bet you need to plug in car for more than 3 days for the light to change to green. I assume you have no malfunctioning lights or stuff plugged in like a GPS cord.

 

i disconnected the battery from the vehicle,,

 

I still think "almost 2 days" is NOT enough time.

 

Sorry,, didn't get that part,,

 

For example, when you close the doors and trunk/hood do the lights turn off? Do you have a Garmin GPS plugged in (even when "off" they still pull power when plugged in)? In other words, you have no additional parasitic draw.

But you say the battery is disconnected and on the tender. So, this should not matter.

 

I have a CTEK battery maintainer and it takes a few days to fully charge the battery even if it's not dead. If I leave the car parked for more than 2 weeks in the winter without the CTEK there's a good chance the battery won't start the car - that's normal. My wife's MINI takes about 30 minutes to fully charge. Our Toyota minivan takes overnight. Every manufacturer is different.

 

Get a "Group 48" Battery, Its Smaller than OEM and usually More Powerfull... If you ask for a Replacement Battery for your 996 at the Store (Other than Porsche Dealer) they will give you a Even Bigger/Heavier Battery than the Factory one... Request a "Group 48"...

My Aftermarket Replacement lasted just over 2 years, it had a 3 year Warranty so i took it back and got a new one under Warranty. My Factory battery lasted about 3 years

 

Just adding my data point. I just replaced my battery now. Autozone specs out a Duralast H8-DLG. When I brought my original battery to Autozone, the Duralast H8-DLG was a bit longer than the OEM battery for my 2004 C4S. Luckily, I asked the salesperson to check with me what alternatives they had. We put my battery next to some other ones and found an EXACT size match. Here are the specs below. It cost me $145 with the $12 core charge ($157 without).

Duralast Gold
Part Number: 94R-DLG
Weight: 47.4 lbs
Warranty: 8 YR
Application: Automobile
Cold Cranking Amps (CCA): 730
Core Charge Applicable: Yes
DIN Designation: H7
EN Designation: 77L4
Height (In): 7.5
Height (mm): 190
Length (In): 12.4375
Length (mm): 315
Width (In): 6.9375
Width (mm): 175
Weight (Lbs): 48.5
Post Location: Top Post
Reserve Capacity (Min): 140
Right Or Left Hand Positive: Right
Voltage: 12

It's a bit pricey but still better than the $250-$300 or whatever Porsche is charging nowadays for a battery that probably doesn't have the same cold cranking amps.

 

A much better buy than a Porsche battery, absolutely.

 

If it's on a Battery Tender Jr., it will take at least two days to go green. My Volvo goes on the Jr. when it has sat for about two weeks and the P-car is on the larger Battery Tender.

 

I like Interstate and I price shopped and found them at a uniform cost until after I installed it and then found it cheaper at Sams