billski

Hi All,
My 79 911 SC wouldn't start yesterday so I pulled out the battery to recharge it. I noticed that No 1 cell was very low so I tried to top it up. I then noticed battery acid running out the bottom of the battery and found a large crack at the back of the battery.
I have been having a erratic tach, and an intermittent charging light as well as the headlights alternating bright and dim. I have redone all the grounds I could as well as replaced the regulator with a new Bosch item. The charging voltage was about 14 volts at 2000 rpm. I have no idea how old the battery is but I am sure that I have never dropped it.
Any ides what could crack a battery case? It has been cold here the past few days by UK standards but I used to live in Canada where it gets just a little bit colder and I have never seen a battery crack before.
thanks in advance
regards
Billski

sc91183

I'm not sure what cracked your battery but that is one of the reasons I recently switched to a dry cell battery,not sure if Optima brand batteries are available in your area but I'm sure there are some brands of dry cell available in your area.Lots of Porsche owners have switched to this style of battery to control acid spills that eat the battery tray area,while others have switched for the longevity of the batteries,I have heard of some people getting 7-8 years out of these batteries!!They are a little pricier(about $100.00-110.00)in the U.S. but well worth it in my opinion.

jlkline

Sounds like your voltage regulator has gone bad and is periodically overcharging your battery, causing boil over and possibly the cracking. (Is the battery of a high quality...factory or Interstate for example?)

Also, if the battery was not well mounted it might have sustained enough shock to crack it as well.

billski

Hi All,
I did just change the voltage regulator a douple of weeks ago and funnily enough I have just received a battery mount in the post that I had ordered as the mount was missing when I bought the car. I hadn't thought of that as being a reason for the battery to crack but it seems obvious now DUH! The battery tray is steel and would be responsible for putting a lot of shock into the battery.
The cracked battery was a Bosch as is the replacement I bought today.
I wonder if having one cell leaking could be the cause for the intermittent electrical faults I have been having.
I will install the mount with the new battery tommorrow and also put a rubber pad under the battery and see if it fixes the faults.
thanks for the replies
Billski

pjc

I have just noticed that I have had a slight battery leak (white powder and disolved paint) and it is a good point about "dry cell" - any UK guys know where they can be had? I assume they come in different sizes and therefore fit the 911's battery mounts?

PJC

ebsalem

dry cell batteries are pretty common in race cars so I start at a race shop. I got mine at a shop that specialize in Dirt Track cars, but they work just fine. one 25 pound battery under each headlight, 900 CCA each.

e

jlkline

Billski, be sure to treat the battery tray area with an acid netralizer before installing the new battery and and netralizing mat. The acid may continue to eat the metal and could require a front pan / battery tray replacement which is a very expensive repair.

I haved used a solution of baking soda and water sprayed through a pump bottle which works well and ensures good coverage.