2mA with a 40Ah battery would take 120 weeks. Are you sure? 5 weeks implies a current draw of 50mA which is perhaps more typical I would expect to see in a car.
A battery would self-discharge in a couple of months without any help from a current draw.
My alarm had a slightly hissy fit when I managed to flatten the battery by leaving the lights on (it would keep going off when I opened the door even with the engine running). It sorted itself out eventually.
My wife's Mazda 2 car battery went flat following a 4 week holiday. National Tyres kindly replaced it with a top range expensive battery. I went flat the other day, I did a 24hr trickle charge.
I've measured the current draw as:
Alarm only: 0.05A Interior Spot: 0.65A Boot: 0.53A
The alarm only ties in with the 4 week holiday. The interior spot ties in with 3 days from when she went shopping.
Car gas been fine since though suspect the 40AH battery is probably
10-15% down at least.Ford Focus 1.8 has had no problems though it is now getting a fortnightly charge as it's going nowhere.
~3% / month they suggest.
I have *several* LA batteries kicking about here and many are left for several months untouched and often only need a quick top-up with a small charger.
Not a very good one for a 68Ah battery apparently.
unusual mode of transport.
The op's data doesn't distinguish between bad battery, bad alternator, excess discharge in the car etc.
NT
I think I am, but I only use the multimeter a couple of times a year so I may have messed something up.
As you an Dave question the reading I will check again tomorrow. I don't think I have an alarm so I guess the only real requirement is the door lock receiver. I'm not sure how much power that requires.
Not just the receiver. The device that provides the timed pulse to open or lock the doors will be live too. Then you have things like the radio or whatever memory. Even the clock.
I've not known any modern car where it is as low as 2 mA.
or 0.20A?
Bill
My point being, your car is two years newer than my wife?s Skoda. It?s unlikely that the VAG group have forgotten how to manage a battery. More likely that the battery is faulty.
Tim
I once left my 1998 Astra F for 7 weeks without using it and the battery was already 6 years old.
It was noticibly sluggish when it turned over but started immediately.
No keyfob locking on that model. The drivers key just locked or unlocked all the other doors, but it did have a factory immobiliser.
Or the vehicle has stop/start technology and has been used for a lot of short trips in traffic, thereby putting a massive strain on the battery already.
OK I just tested again.
Procedure:
Undid black wire from battery. Tightened black wire on to ammeter probe. Connected ammeter com probe to battery neg terminal (with elastic band) Used Amp setting on multimeter.
Initial reading ~0.6 A. After about 90 seconds this dropped to 0.022 A After another 60 seconds this dropped 0.004 A Remained at 0.004 A for another minute of two, until I got bored.
Tried pressing key to lock. Again power jumped to ~600 mA After about a minute or 2 it dropped back to 3-4 mA.
Tried same stuff on ammeter mA setting. Same result. The low reading was oscillating between 3.67 and 4.99 mA.
So slightly different for the 2 mA I read yesterday and I admit to a fair bit of user ignorance, but I can't see what I have done wrong. I think the reading is genuine.
Obviously a real test would require an average reading over an extended period.
5 weeks = 840 hrs
68 / 840 = 0.28 A or less than 4 Watts.
OK a very rough guide but shows that even a low drain will
*completely* flatten a moderate capacity battery in the time scale in question.
Cars with stop/start have a larger battery. And starting a hot engine - especially one which has been designed to re-start quickly - takes very little from the battery.
The stop/start is disabled until the car decides it's OK to use it.
Yes, not unreasable I suppose, considering all the bits and pieces connected.....Got the battery in the house now charging, using a 19v x 4A laptop PSU and a 55w Headlight bulb in series, the charging current dropped from 3.6 amps to 2.8 amps fairly quickly and seems to be staying there. I will give it while and then put in another series headamp bulb in to reduce the current to ~ 1.4 amps. I should then be able to leave it over night adjacent to a small open window.
All seven of the battieries in my motorhome need very little charge after sitting (isolated) for months. And when you get a new battery from the battery shop it never needs much of a charge.
Bill
Hmm, the problem with that solution is that while you are limiting the current, you aren't limiting the voltage and it *will* gas quite heavily during the balancing phase (as it tries to reach 19V).
Now if this is a wet battery with recombination vents it may not be a problem but if it isn't, it might be.
Unless you are doing this for fun on a spare / old battery? ;-)
Cheers, T i m
Quite (7! ;-) )
SLI batteries may have a higher energy density than a real leisure battery (designed to tolerate a greater DoD) and certainly more than a traction battery but I'm not sure if that has any bearing on their self-discharge characteristics?
I would have thought the higher the energy density the higher the level of self discharge (for the same nominal capacity), irrespective of the construction (tubular etc)?
I think the biggest factor is the parasitic load and with many traction / leisure scenarios, they can be / are removed completely when the vehicle / vessel isn't in use.
Cheers, T i m
Hydrogen floats to the ceiling. If you were accumulating gas, it fills from the ceiling down.
I collected some in the basement once (not intentionally), and it was quite interesting how thin a layer it formed. Maybe 6" to 8" cloud below the floor above. Before it exploded. And nobody upstairs came running down to see what happened :-) That was the best part. They must have heard that.
You may find that the open window trick, isn't enough.
When my next door neighbor charged an automotive battery and closed the garage door, my suspicion was it was the light switch on the garage wall, near the side door entrance, that set the gas off. Since my neighbors garage was a shit hole anyway (he was a welder by trade and did occasional work at home), it was hard to tell what might have been battery damage, and what was there already :-) He claimed there was acid about the place, but I didn't see the battery when I did my little tour, so didn't have a chance to see whether the battery interacted or not. it might have just been the gas nearer to the ceiling.
I've had some other close encounters with hydrogen. It singed my eyebrows once, as the flame went up past my face. Some people just never learn :-)
*******This is the result of todays experiment charging my car battery. The battery in this case, might be "good" for a change, as the end voltage wasn't all that high. I've had batteries that rapidly went to higher voltages, indicating the battery wasn't all that good while charging.
11.8V OBD2 "VLT" key at first position 11.5V OBD2 "VLT" key at second position, fuel pump runs The trick with OBD2, is avoiding incidental electrical loads, as a result of plugging in. 12.20V meter@battery car sitting for a few days 12.67V car back from 50 minute drive I expected it to charge a little higher...3:21 2.50A little smart charger starts cycle
4:20 14.52V 1.12A 5:10 14.52V 1.10A 7:05 14.56V 0.84A 8:43 14.61V 0.62A Missed the shut down and charging complete9:50 13.35V 0.3A Charger claims to be off, still pumping current??? Something is not adding up there. Car courtesy light is in manual off position, so there's no load that way, and when charging started, car was locked the whole time. The idea being, not to disturb the smart gizmos in the car. I charge the battery, in-circuit. Car quiescent load, is somewhere around ~10mA (last digit of display on 40.00A range, so not a high quality measurement).
Anyway, it looks like the charger was doing some sort of "topping up". I had expected the current to be a bit higher near the end. (What's the point of a smart charger, if it isn't doing non-intuitive things ?)
It gives the impression above, that the battery is "behaving a bit stiff" near the end, as I would have expected. If the battery rose to 15.5V or something, then I'd know there was trouble. Charging bad batteries manually, it was pretty hard to tell what a "reasonable" value should be.
The smart charger is supposed to pulse in a bit of current, and check the relaxation behavior, as part of determining how things are going. Flipping my clamp-on ammeter to "Hertz" showed rather random numbers, implying a pulse waveform might well have been present. Even though when set to the DC range, the value seemed quite steady when measured that way. I don't have a scope, so can't verify what it's doing.
Paul
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