Grandad wrote:
I wonder if the people who get a flat battery without the engine running also go out every few minutes when they are at home and not working to run the engine to stop the battery getting flat.
If their battery goes flat just by having the engine off for a few hours would suggest to me that they need a new battery.
I would certainly agree that those ending up with a flat battery on the ranks are unikely to have one that's in tip top condition, but apart from that...
I mean, for a start, who replaces a battery until there's evidence it has deteriorated significantly? Not many, I'd guess, and certainly not me. Not that I wouldn't replace it if I was having starting problems, or whatever, but I've run with batteries that I know aren't in optimal condition, and act accordingly, but sometimes make mistakes and have been caught out
Which is probably what's going on with these guys on the ranks - they've been on the rank a few hours, not going anywhere, maybe just starting the engine a couple of times for a very short period to move up the rank. Meanwhile, they've maybe got gadgets running from a 12V adapter, they've put the ignition on to put the window down to talk to someone/get some air in the car, or whatever, they forget to switch off the ignition, blah, blah...
One driver I knew would often have his ignition on and heater fan blowing to clear the screen of condensation in the rain, and would use the wipers to clear the screen at the same time. Not something I'd do myself other than for a very short period, and he was never caught out, but if his battery wasn't good and he did it a bit too often, then...
But (Grandad) you can't really compare sitting on the rank - even without much in the way of power hungry stuff in use - with a car sitting locked up? I mean, weren't you the one further up the thread suggesting the use of a 12V heater in the car?
A locked up car's draw is probably less than 1W, while the heater you linked to is 150W alone
Thus the heater alone is the same as maybe 30 sidelight bulbs, never mind any other stuff that might draw current in a car on the rank, such as heater fans, ignition being on, windows etc. And that's just the very hungry stuff - interior lights, the rooflight and also the meter can all add up over several hours.
Here's another reason a car locked up is maybe not comparable to one on the rank. Maybe twenty years ago, I knew my battery wasn't good, but was short of cash and just tried not to run it down. But never had a problem starting it from cold.
But a couple of times I caught myself out on the rank, and the car wouldn't start. But a few times I got round that by simply switching everything in the car off (stereo, meter, rooflight, interior lights, or whatever), and after maybe twenty minutes that would somehow replenish the battery enough to start the car
Not sure precisely what that was all about, but even switching off a few 5W bulbs, the meter and stereo seemed to allow the battery to somehow recover enough to start the car
But even ignoring that, I don't think comparing a car locked-up for several hours with one on the rank is really comparing like with like, particularly for a driver who maybe uses lots of gadgets while in the car and is maybe a bit careless.
(B&H are right insofar as there's a CGAF element of drivers (particularly part-time types who don't own the car, say), who will idle excessively. By the same token, the CGAF element are maybe also the type who will leave the ignition on too long, and/or run lots of gadgets etc, and any possible issues with the car and its battery are just ignored and left to another driver.)
Apart from that, I don't have any particular view on the subject
(Was going to maybe look at the thing historically, and that maybe more modern batteries are better than 20 years ago. I've got a big capacity stop-start AGM battery, so charging a phone or whatever isn't maybe the same problem it might have been twenty years ago. By the same token, my VWs' 12V sockets wouldn't work without the ignition on, which years ago I regarded as a real pain, because obviously having the ignition on was increasing the draw on the car battery while stationary.
But it's not a thing I've thought about for years, because batteries on phones etc are a lot better these days, so can't really recall the last time I used my 12V sockets for anything, assuming I've got my phones charged up before I go out. And now got a 1,500A Noco jump starter, which I've used occasionally to charge my phones or card reader (and customers'). It supposedly also jump starts diesel engines up to 4.5 litres and petrol engines up to 7.0 litres, but I've never used it in anger yet, so don't know if it will work
But if anyone with a 1970s Jensen Interceptor needs a jump start, my Noco Boost would manage the 6.3 litre engine, but not the 7.2 litre one. In theory, at least

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