Battery Draining

[Phoenix]

Ok, so this has happened twice now which for me puts it out of the realm of happenstance.

I keep both batteries on my 73 911t on battery maintainers whenever the car is parked and have done so for the past few years. I haven't been driving it much lately as work and family responsibilities are keeping me too busy. Yesterday after a quick 5 min ride to Home Depot and sitting for 15 min while I was inside, I returned to a severely drained battery. It cranked twice and then started with the dreaded "click, click, click..."

Called the wife who brought the Subbie for a jump. Once connected the car started and ran just fine. Once home after a 5 min ride, shut the car off and restarted 3 times, the last 2 were slow cranks as if the battery were drained again. After a few hours on the maintainers, both maintainers showed fully charged and the car seems to crank just fine. A similar situation happened 2 weeks ago which leads me to believe something is not right.

The only continuous drain I'm aware of is the clock, though the maintainers are always connected.

Any thoughts?

[docrodg]

Could be alternator output is low. From your description the car is fine if kept in a charged state, once run it kills the batteries. Also check both batteries, one may have low cells.

[dad911]

How old are the batteries? What is the voltage while running (charging from the alternator)?

[pozee]

Phoenix,

Here are some possible causes:

1 - Old, weak batteries.
2 - Poor terminal or ground connection/s.
3 - Starter motor or solenoid on last legs (not likely).
4 - Charging system failing (not likely).
5 - Battery maintainers not maintaining batteries (not likely).

If I were you, I would bet on 1 or 2 or both.

Good luck.

[Phoenix]

Thanks you for the tips.

I went out and picked up a multi-meter to start diagnosing.
Both Sonnenschein batteries are fairly new (less than 1,000 miles) and read 13.3 volts when the car is not running and 11.4 or so when it is. This leads me to believe they're not the problem.

The lights, clock and fuel pump all seem to be working just fine, If I hold the key in cranking position, the motor does turn over though extremely slowly. The longer I hold it, the slightly faster it gets.

I'm starting to suspect it may be the starter itself.

[ossiblue]

If IIRC, with the car running and the charging system at full operation, your numbers should be reversed, if anything--13+ volts while running and (ideally) 12 volts with engine off. Did you typo the numbers?

[kidrock]

Originally Posted by Phoenix

The lights, clock and fuel pump all seem to be working just fine, If I hold the key in cranking position, the motor does turn over though extremely slowly. The longer I hold it, the slightly faster it gets. I'm starting to suspect it may be the starter itself.

+1......if your lights and other electrics are working well, and your starter is operating slowly (or click click clicking), it sounds as if you may have a starter on it's last legs. Before you replace your starter, make sure your connections at the starter are clean and tight.

[Wil Ferch]

quote..." and read 13.3 volts when the car is not running and 11.4 or so when it is. This leads me to believe they're not the problem...."

Factoid....with car "off"....12.6V = 100% charged battery
12.4V= 75%
12.2V= 50%
12.0 V= 25% charged
<12 V= dead battery.
Battery seems bad and/or charging system not keeping it charged.