OT: Magna battery draws 0.08 Amps when not running

[danlb]

I was surprised to find that our car does some emissions based self tests after it's shut off. Don't quote me, but I recall that one was a vacuum leak-down for the fuel system. I became curious and looked into it after my wife pointed out odd noises after the car was parked for a while.


Dan

[Norman Bain]

Thanks to all for engaging on the topic.

I like the option adding in the battery isolator as described by PSTechPaul ... will order one of those as it lets novices turn off the draw on those occasions when needed. I am not concerned about turning "off all electrics" and restarting same as this has happened many many times over the years without issue.

I do note that the motor does get a little ragged at idle when the battery is close to dead ... but comes good as soon as good power supply is restored.

The battery is (now) new so there should be no "wicking" directly across the terminals causing leakage. That does not mean that wicking is not occurring elsewhere.

My multi meter has a 10AMP plug point and that is what I have been using to get the reading thus far.

The car has had a couple of runs with new battery since I posted the question. Today I setup the multi meter before detaching the battery cable in an attempt to get a "fresh and settled" reading. Did not work ... clip fell off and dropped the connection ... however I do note that it is now 12ma for about 30 seconds or so then drops immediate to 5ma and stays there.

I think from the posts that all is good for me. Thanks again for providing analysis and instilling confidence.

[PStechPaul]

The battery has become indispensable to the running of modern car engines. When the battery in my 1999 Saturn totally died, I got a hot-shot that allowed it to start and idle, but as soon as I put my foot on the brake to get ready to drive, the engine died because of the additional load of the brake lights. When the battery failed in my 1989 Toyota pickup, it ran terribly and overheated in the 2 mile trip to my mechanic, probably because the fuel injectors were screwing up the mixture.

[darryl]

One of my jobs today was to troubleshoot a camper/trailer for draining the battery too quickly. Turns out the fridge needs 750 ma to remain in operation, and the battery had been drained enough times that it didn't have anywhere near the capacity it should have had (mostly trying to keep the fridge cold). It's an LP fridge, but has a control module to sense when the burner is working. It also runs a gas valve. Between the two the drain on the 12v system is considerable.

Considering also that the on-board charger is voltage limited (to prevent boiling off the battery) it doesn't ever deliver enough voltage to bring the battery to full charge. This is probably a reasonable trade-off in this use, but you do lose something of the full capacity. I'm going to put it on a trickle for a few weeks to see if it helps- I've had some luck doing that with other batteries.

There's also some leds that remain on in the system- not much loss here but it's still a drain. My Land Cruiser could sit 6 months and still have a good charge- enough for an extended cranking to get the old engine running- but there were no parasitic drains. Sometimes simpler is better-

[PStechPaul]

It would be good to have a low voltage cut-off that completely disconnects the battery from the vehicle circuitry (except starter) when the voltage goes below 11 volts or so. Another option would be a separate battery for accessories and ECU. RVs often have such a system.

[darryl]

This particular camper/trailer has a fairly long boxed-in area to carry the battery. I don't know if two Trojans will fit here side by side, but it looks as if they would. That was my recommendation anyway- two 6v Trojans. The other option would be a second deep cycle battery and a disconnect for each one. That way you could have one fully charged battery available in a pinch.

The low voltage cutout is a good idea- I don't know if this particular unit has that feature, but there's no circuitry visible to suggest that. In any event, if a battery is discharged to that low level, it should be brought back up to full charge as soon as possible.