MGB: Another Reason I Like Old Cars

Having just had to recharge the battery in my modern transportation that is temporarily off the road because the readio presets ran the battery flat (in summer we use one regular vehicle plus a couple of collector type cars; in winter we run two 'regular' cars) I like my old British stuff even more.

The MGC can sit there all winter and the battery spins it over just dandy when I want it to! Amazing that the small draw from a radio sitting there turned off can drain a battery in 2 weeks or so!

Sounds like you have a bigger drain than just the radio presets. I left my Jeep(2000 model) sitting for six or so months, hopped in, and cranked it straight away. Red top Optima is a grand battery;)

Might want to check out your electrical system!

We have a "modern classic" and it has a very large engine that cranks over with no trouble after a couple of months in this arctic Chicagoland winter.

Well it may have been a month since I last started it, but it is also a new battery.

Aside from the radio, I don't know what would constitute a draw - the ECM isn't supposed to pull any current with ignition off, is it? Or is it?

bills Wrote:

Quote: "
Well it may have been a month since I last started it, but it is also a new battery.
Aside from the radio, I don't know what would constitute a draw - the ECM isn't supposed to pull any current with ignition off, is it? Or is it?
"

Nope. Sounds like you have an electrical problem.

That being said, my Mustang (08) GT would kill the battery in a month if it wasn't run.

Yes- ecm will draw a little. At least with OBDII. Now that I think about it, OBDI too. No power, trouble codes would be lost everytime you turn off the car. OBDII also "learns" the driving conditions from the sensors. When power is lost, it has to re-learn. Also, does your car have key-less entry, or alarm? It has to continuously "listen" for your signal to unlock, or disarm.

Forgot- do you have an added amp? they too draw power when "asleep". It does add up, but 2 weeks does seem a bit too quick.

Lead/acid batteries will self-discharge at about 3%/month. So 6 months shouldn't be enough to prevent them from starting the car, it should still have 80% of it's original charge. Anything over a year, maybe, but 6 months, no.

The Optima AGM battery self-discharges at a fraction of that rate, probably less than 1%. AGM batteries are a great choice for anything that may sit idle for extended periods.

I've seen bad switches in trunks and glove boxes that cause lights in those areas to remain on and run batteries down. You could put an amp meter on the battery and measure your current drain. Radio presets would be a few milli-amps, which wouldn't drain a AAA battery in a year's time, much less a car battery.

Yeah, I'd guess you have some other drain going on.

It's funny, the OBD1 in the Fiero (the car that drains the battery) is similar to the ECM I use in the Jamaican, which doesn't seem to drain as fast, but AFAIK there is nothing else on the Fiero that constitutes a drain. No alarm, no switches left on. It does have a factory bass amp in the system, mind you.......

Steve Lyle Wrote:

Quote: "
....
I've seen bad switches in trunks and glove boxes that cause lights in those areas to remain on and run batteries down. You could put an amp meter on the battery and measure your current drain. Radio presets would be a few milli-amps, which wouldn't drain a AAA battery in a year's time, much less a car battery.
Yeah, I'd guess you have some other drain going on.
"

Good point. I had a bad power lock switch in my Grand Marquis that drain the bat within one week. My locks didn't work (I removed the motors), but the relay to the motors stayed on all the time. I found it by removing the + bat cable, putting an amp-meter between the bat and cable, and pulling the fuses 1 by 1 until the current draw went to almost 0. Checked the schematic to see what was on that fuse and went from there.

bills Wrote:

Quote: "
, no switches left on.
"

Nothing you currently know about. With a new battery, a quality new battery, you should be able to leave that car sitting for much longer than a month......something else is discharging your system,....you're just unaware of it at the moment.

My wife's Cadilla CTS can and has run the battery down in less than two weeks. Cadillac recommends a trickle charger if you're going to leave it unstarted longer than a week. If you pull the cable off the battery with nothing on, there is a good strong spark, indicating that a lot more than a radio memory is running all the time.

Yeah, the way to check is to put a meter between the battery and car. Haven't done that lately to check draw - suppose I should.

bills Wrote:

Quote: "
It's funny, the OBD1 in the Fiero (the car that drains the battery) is similar to the ECM I use in the Jamaican, which doesn't seem to drain as fast, but AFAIK there is nothing else on the Fiero that constitutes a drain. No alarm, no switches left on. It does have a factory bass amp in the system, mind you.......
"

A factory amp will do the same as an aftermarket amp. If the final amp is not built-in the radio, you have another current draw, a small one, but still a draw.

Are you sure there isn't a light somewhere (glove box, door bin) that is staying on? That will not show up until you leave the car for a week or more.

Clocks,radio presets, and ecm's all draw only milliamps of current. You have another problem if battery is dying in less than 3-4 months minimum.

sws615 Wrote:

Quote: "
Are you sure there isn't a light somewhere (glove box, door bin) that is staying on? That will not show up until you leave the car for a week or more.
"

Yes, first thing I checked. No glove box in these, and the front and rear compartment lights shut off properly.

Might be interesting to disconnect the bass amp and see what difference that makes!

Yeah Scott, My Ex has a 06 Stang. It sat all winter since she was ill. Ruined the battery. I know it was 3yo but I think if it wouldn't have been left discharged, it should have went longer. My Harley has a security system and it will drain the battery in a month too.

Probably the simplest solution would be a cut off switch if there's room to mount one.

I stongly recommend a battery cut-off switch conveniently mounted.

Battery Tender. Internal smarts allow it to be connected full time without harming battery. About $39.

Edd Weninger Wrote:

Quote: "
Battery Tender. Internal smarts allow it to be connected full time without harming battery. About $39.
"

Well yes...except.....

I have one garage, one port cochere (that will cover two cars) and 8 cars at home (and one in storage - for obvious reasons).

Electrical cords running all over the place would constitute a hazard, not a convenience. I just have to remember to disconnect a battery cable when leaving one for a longer period.

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