Easy way is to get one of those battery disconnect devices. It fits between the battery ground terminal and the ground lead. You unscrew a knob to break the circuit. So you can connect your DVM across it, wait until things settle, then unscrew the knob.
With the battery disconnected I've left a car for up to 12 months without problems.
Yep, need radio reset code first, some alternate alarm system and away we go. Don't you just love modern technology!
Absolutely no different from allowing the battery to go flat.
I doubt you'd much like a daily driver that didn't have any electronics.
I've lived with several without any problems. The only genuine & worthwhile upside of vehicle electronics is better mpg.
NT
You jest? My last car only had one new set of plugs in its life. And
15,000 miles service intervals. Which was mainly simply an oil change.
I had this very problem on an Austin Healey Sprite and after much multimeter investigating I found that the horn was draining the battery. I can't remeber the current draw but it was very small but enought to prevent starting after a weeks standing idle in cold weather. I disconnected the horn, ran the car to charge the battery, left it for a week and it started no problem. A replacement horn from the scrap yard was then installed and the car continued to perform as it should for ages afterwards. Mind you, no electronics involved in that car, but no anti-lock brakes either.
- Mike
Car batteries don't like being left that long without being charged.
A mate of mine had the same problem with a (simple, old fashioned) radio. Taking 50 mA or so even when switched off.
A lead acid will be fine for a very long time if fully charged before disconnecting.
About half that would be realistic.
Bill
Lead acids last longer when discharged at a slow rate than their 20 hour capacity. What is nearer half that is the discharge from not-full to still having enough juice to start a car reliably.
NT
It had gone flat enough that the car wouldn't electronically unlock but not enough to stop the radio from working.
One of my big regrets is selling my Triumph TR2.
Running a battery that low is likely to shorten its life. But pretty inconvenient if it is so low it won't start the car. Surely easier to enter a radio code if needed?
Hardly a daily driver for these days, though? ;-)
I also missed my Midget. Which I sold in the early '70s. So recently treated myself to a used Boxster. And am enjoying open top motoring again. But with much less of a draught than older designs. ;-)
Exactly, which is why I said above that I need to get the code first before I start disconnecting the battery.
The dealer has agreed to do this for free and I'm popping in tomorrow. However it still leaves the car without alarms if the battery is disconnected.
As the cars are on the driveway I've wondered also about a trickle charger and run to both cars in parallel. Presumably any standard household wire would suffice to run the lengths from one car to the next?
As does the battery running flat.
Both Lidl and Aldi have excellent chargers on offer a few times a year. They cost about £13. More than powerful enough to charge a battery overnight - then changes automatically to a maintenance charge which can be left on indefinately. Small enough to fit in a large pocket. Ctec do a similar charger - but at about 3 times the price.
I'd not use one charger for two batteries long term. Any difference between them may confuse the charger. And at that price hardly worth the bother of trying to rig up two from one.
I have one of those chargers fitted permanently to my old Rover, which is parked outdoors. Fitted a waterproof mains socket mounted under the bumper to power it. It's a small Bulgin Buccaneer, and near invisible when not in use. Made up a special mains lead for it which plugs into an outside 13 amp socket.
No, use two chargers.
Bill
It isn't such a good idea to connect car batteries in parallel with thin wire unless there is a fuse somewhere to protect it. The short circuit current is in the 100's of amps. Wire red hot almost instantly.
You might want to consider a solar powered trickle charger that although no great shakes for power output or routine charging will easily provide around 50-100mA of top up current on a sunny day. eg.
(as an example not a recommendation) I'd be inclined to go for ~5W.
Plugs into the cigarette lighter and in summer at least holds the battery charge up against the base load of ~30mA and self discharge.
Useful for cars that don't often get a long run (eg short commute) but spend a lot of time stationary in the sunshine.
Of course all the door locks get mangled as well no doubt. In the long run maybe just a trickle charger is best. Brian`
Neighbour had one on his little used 911 Porsche. Noticed it when the AA were jump starting it. Again.
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