dfinnegan

Interstate as Indycam noted.

I tried to have the old battery load tested. Despite a claim that they *could* do a load test there was only an electrical meter type device and the report was that the battery was showing 12.2 V (or was it 11.8?) and 535 CCA out of a spec'd 700. It took all of 10 secs and was not a satisfying result. I ended up leaving the battery with them. $10 in my pocket vs a hunk of lead and acid in the corner of my garage; I actually struggled over the decision!

I haven't checked the voltage against rpm due to time constraints.

I will continue to test and post results as I gain them.

Cheers

dfinnegan

The car has been sitting for 11 days without the battery tender connected.

Today I measured 11.50 V and 23.8 mA draw.

Seems to suggest that the battery was bad, but I'll keep an eye on it just the same.

For those with a bit more electrical knowledge, how does that 23.8 mA draw compare with 11 days and roughly a 1 V drop? Just curious. Thanks.

Indycam

As your car is off the road for a bit , pull a cable off of it , charge it all the way up , don't reconnect the cable . Test the voltage after 24 hours . Test the voltage again after 11 days .

dfinnegan

I can do that.

So, you are suggesting:

Fully charge the battery.
Note the voltage.
Disconnect it from the car.
Measure voltage after 24 hrs.

Then, connect it back up to the car? or leave it disconnected?

Measure voltage again after 11 days.

Indycam

Undo one cable .
Fully charge the battery .
Disconnect the battery charger .
Wait 24 hours , then test the voltage .
Wait another 10 days , test the voltage again .

If you test the voltage right after the battery has been charged , that reading is misleading .
That test gives you what is called , the surface charge .
You need to wait 24 hours after the charging is done to find the real voltage of the battery .
Waiting 24 hours will let you see the real state of the battery .

Waiting the 11 days will show you what the self discharge voltage is .
what your battery would have read if it was not hooked up to the car .
With the battery hooked up to the car for 11 days it was down to 11.5 .

darth

Dear Dfinnegan

I'm not sure, not knowing the A-H rating of your new Interstate battery, but the 11.5 volts after 11 days seems low. Did the engine crank over OK when it was at 11.5 volts? I don't think 23.8mA will cause the voltage of a fully charged battery to go down that far. Do you know what the battery voltage was at the start of the 11 days? How are you measuring the current? I would have thought the voltage would be above or closer to 12 volts after 11 days, provided it started out at or above 12.6 volts. Either there is more current being drawn when your not looking or the battery isn't charging fully. I'm assuming the battery is good since it is new and you've checked/cleaned all connections to the battery and the alternator/starter, including ground straps or where battery cables come close to moving chassis parts and there's a chance of insulation wearing, all of which could affect charging/discharging. I would suggest repeating the same charging test you did on the old battery, especially around the 4000 rpm area, where you witnessed the charge voltage to decrease. All your battery problems maybe due to the battery not charging fully.

Bill

Lorenfb

No use battery calculation:

Assumptions:
1. 75 amp-hr battery (basically an average capacity)
2. 30 ma current draw (typical for a 964/993 key-off & electronics 'asleep')

Conditions:
1. battery at 3/4 capacity to allow good cranking & proper ECM voltage
2. no charging nor starting for time period

Time = Amp - Hour rating / current draw

Time = 75 X .25 / .03 = 625 hours =~ 26 days

dfinnegan

Fully charged battery
Disconnected it
(failed to check voltage 24 hrs later; I've been traveling a lot)
Left disconnected for 5 weeks
Measured voltage at 12.65 V
Connected it
Left for 10 days
Measured voltage at 12.38 V and 26 mA draw

Indycam

So that tells me the battery is not self discharging .

dfinnegan

And, it's losing just 0.27 V in 10 days while connected to an inactive car.
And, the car is drawing just 26 mA while inactive.

Suggesting that my previous problems were related to the old battery and perhaps some faulty diagnostics on my part; such as failing to let the ecu settle after disconnecting and reconnecting the battery.