Starting issue - battery related
 

'85 3.2. Drained the battery (by leaving fan running.) Took battery out and charged to 11.7 v. Barely turned over. Did a hill and poped clutch and started... then died. Seems to me 11.7 volts would be sufficient to crank nicely... but not sure about that. Engine started & ran fine before battery drain. Is it too low on volts or is there something else going on here that I need to check?

A fully charged (and healthy) car battery should charge to 12.6 volts -- if you can't get yours to charge to that voltage, your battery is likely now damaged/faulty (which can happen when a lead-acid battery is allowed to fully discharge) and will prevent the battery from delivering the current it otherwise would . A FLAPS should be able to test your battery and confirm -- this thread (though from a Mini forum) provides some good clarification https://www.honestjohn.co.uk/forum/post/135194/mini-one---11-9v Out of curiosity, how old is your battery?

Darrin... thanks... Read through that thread. Age: it's old enough that I forgot when it was had. Maybe 15 years old. Is one of those DieHard MONSTERS. Am going to try a jump this eve. If that doesn't get things rolling... new one seems inevitable.

if already 15 years old, I wouldn't waste your time -- it's dead -- consider getting a slightly smaller/lighter Group 48 battery (our cars' battery trays have a mount to accommodate that battery too). I'd also strongly recommend going with an AGM battery, as its new(er) technology makes it a lot harder to leak acid in the battery tray during an overcharge (failed voltage regulator) situation

Old battery.........
 

Karl,

You have been fortunate that you did not get stranded somewhere with your old dying battery. I would be happy to get 10 years service for any of my car’s batteries. But 15 years service would be incredible. Do yourself a favor and get a new replacement battery. How long to do you expect this 15 year old battery to last? The health or strength of a car battery is measured in CCA (cold cranking amperage) and your local auto supply could test it for free.

BTW, spend some of your money to help the economy grow. You are too frugal like me but I am broke. Stay safe and healthy.

Tony

Thanks Darrin!


HA! With all the 911's you have stacked up... you're only conceptually broke Tony!

Am now indeed motivated to step out of the old lead and into some new---thank you guys!

ps---car batteries should last forever ;)

.

A few symptoms to note for anyone finding this as a search result...

• After the battery died, tried to pop the clutch on a steep hill (which has worked before on a weak battery) and nothing.
  
• Then tried to jump start with supporting engine rev'ing at 3k... got barely a crank. (In nearly 30 years owning this 911, I've never experienced the car not starting on either a pop or jump. Was slightly unsettling.)
  
• Did a 2 amp 12v charge (battery out of car) for a few hours and got to 11.7v. Installed and nothing.
  
• Tried to pop clutch again and got a start, but engine ran barely for a few seconds... then conked out.
  
• Did overnight charge and never got to 12v.

This is the fault of my wiring oil cooler fans to a non-ignition fuse... and forgetting to turn the fans OFF. Am going to change that wiring tomorrow.

Supposedly there are ways to restore a totally drained---sulphated---car battery. With everything else already on the menu, am not going this route. Rather replace it. With approximately 15 years on the old DieHard, that being with minimal maintenance---cleaning electrodes on occasion and perhaps topping the fluids 2 or 3 times in total---I bought into a DieHard Platinum AGM (TY D) from Advance for $180. They deliver free, and did so amazingly fast. They have a $20 core charge that is credited when old battery is brought to store. New one is slightly smaller than prior DieHard with a touch more cold cranking power.

All good now?

Yup!

Karl,
The AGM battery is a great choice. Let me relate my recent adventure with an
AGM battery. Couple of months ago I put my 911 to bed for a while, couple
of days ago went out to start it, and nothing.
Checked with meter and it was flat ZERO volts. (turns out my fault, more later)
Hooked up my small charger in AGM mode. Nothing happening, no charge, yikes.
Worried I had ruined a one year old $160 AGM battery.
So I connect AGM battery with jumper cables to a fully charged 12v battery. After
a half hour the AGM read 5-6Volts. Then hooked up my AGM charger and left it
overnight. Next morning my AGM battery now shows 12.7V.
Breathed sigh of relief that everything recovered. Has held a charge now for
a few days. I don't know if an old flooded lead acid battery would have recovered,
but the AGM did!
When I hooked everything up to start the car, I found my dumbazz mistake.
I immediately noticed my left turn signal light was lit. Yup, when I put her to bed
I somehow had left the left turn signal switched on in that "German park by the side of the road mode" and the small lights had drained my new AGM flat after two months. Won't
make that mistake again!!
I would recommend you acquire a maintainer/charger with AGM mode.
Most newer ones have AGM mode.

Grant