The only way you will know for sure thats its not a power draw from something not shutting down etc is to put an ammeter in series with the battery and monitor it for a period of time as it sits.
When I bought my XK8 it had been sitting for at least a year or 2. The amp didn't go bad from sitting and it killed the battery in 2 days or less. I think the car was parked because of that problem and nobody took the time to troubleshoot it.


Dave

 

I'm familiar with electrolytic capacitors going south on, for example, vintage audio gear, but had not heard of this icw our cars. Any more info available?

If I understand right, the idea is not that keeping power on will prevent this, but rather that if we ever remove power then the required re-boot might fail. Correct? But if this is so, then it seems we also would have to avoid a hard reset on such cars, or a battery swap w/o a temporary power source during the swap. Maybe I misunderstand the point.

 

Wayne,

12.50 sounds good to me. Not like a new battery, but serviceable. At the rate you described it falling, I thought it would end up lower.

I won't pound the table on this further, but if any significant resistance has crept into the charging path it might effect how long it takes to charge the battery, but not the final charge achievable. Also, you'd have other symptoms.

When you re-install the battery, if it discharges quickly then I think Dave's idea is very likely the right one.

Hang in there; you'll get it.

 

Let's remember that when doing a parasitic voltage drop test on a modern automobile an ammeter is placed in series with one battery cable. Then you allow 45 minutes for all the devices to go to 'sleep' before taking a reading (most cars won't need that much time but quite a few do.) Don't forget that switching on a battery tender, while not a draw, will still cause every device to 'wake up' (it is still a voltage fluctuation. Some cars - turn on the courtesy lights, be ready for a security alarm, etc., etc.) That awake state may actually draw 2-3 times more than that little 1.5 amp battery tender. It will take that much more time for it to replenish the battery back to the state it was in before beginning to make any additional headway.

Best bet? Put the charger back in the trunk where there wasn't a problem.

 

IBeav, Now that is what I'm talking about. I see the light and it looks like I had it figured out, but didn't know why. You my be BFF, LOL.
Thanks Beav, as this may or may not be the case but makes a lot of sense.
I will get the battery installed tomorrow and we shall watch it like a hawk.


Wayne

 

Point of order, please. What is shown as a quote from me in the post #24 is not what I posted, but rather a mix of my post, and somebody else's (Beav's, I think) comments and disagreements. Post #18 is what I said. I think we're all entitled to have what we post quoted in tact, if it's to be identified as a quote. I'd appreciate if this could be sorted out. But it is what it is, I suppose.

It's hard enough being responsible for things that I actually did say.

But on to the subject at hand ...

- After charging, it's better to wait 4+ hours and read rest voltage than to get a reading after a quick bleed of surface charge. This is so because rest voltage gives a more accurate measure of the battery's state-of-charge. If we have time, let's do the best measurement possible. See for example batteryfaq.org, batteryuniversity.com.

-Where we connect the charger -- at the battery vs. the engine-compartment (front) terminals -- will not effect what's going on here for the reasons shown in post #18. Easy to verify with a DVM; there is zero resistance between front terminals and battery.

And yes, of course we have to remove the charger no matter where it's connected, while testing for parasitic voltage drop. As far as I know, nobody has suggested otherwise. Nothing to do with a full-time battery tender, so descriptions of a charger interfering with the parasitic test ... I can't follow.