Flattened car-battery charging my phone.

[mointainwalker]

Recently I left my phone on charge inside my car - engine not running, but with radio turned on with no sound. When I returned 75 minutes later the car battery was flat, only showing dash-lights which then also disappeared when I turned the key a second time.

The battery is at least 5 years old but in seemingly good condition that I never have any problems with it: I had driven about 600 miles in the preceding two days so would have expected it to be well charged.

My question is obviously, how can a 2Ah battery flatten a 60Ah battery so quickly ? I do recall a similar incident back in the late 80's where I sat listening to the car cassette-player for more than an hour and was also taken aback when that also flattened the battery.

 

[Burnerman]

Most car ‘infotainment systems’ (horrible term) have a minimum drain of around 2 amps......this escalates dramatically if you have the volume cranked up or it’s searching for data or whatever. The systems go to sleep after around 15 mins, and may instruct you to start up the engine before you switch it on again. Why these systems draw so much juice is beyond me - but clearly they do.
If you have your ignition switch just on one click, then other systems may become live.
Domestic systems use much less current but I don’t know why this should be - apart from the voltage difference.
I left my bike sat nav on overnight once, and the bike battery was completely flat the next morning!
Clearly modern batteries have very little current in reserve, but if your car starts well in the winter where you live, there’s nothing wrong with it.
John

 

[cdbe]

I once wired up a Bluetooth hands free kit to my car - I wired it to a permanent live thinking what harm could it do? Firstly, when the car was on the drive it picked up my phone in the house so I got no sound on my phone. When I figured this out I just turned off the Bluetooth on my phone and forgot about the whole idea. There followed a plague of flat battery issues - generally when the car hadn't been used for 3 or 4 days, I put this down to an old battery and eventually replaced it - when the new one did the same I metered it for parasitic drain (which the was a bit of) and remembered the Bluetooth kit - stuffed inside the dashboard and running 24/7.

 

[JohnD]

Recently I left my phone on charge inside my car - engine not running, but with radio turned on with no sound.

So you had left it in "Accessories On" status.

Apart from the radio, all sorts of things were "on". Maybe the heater blower. you mention the dash lights, so sensors and the instrument panel. Not just the phone charger.

 

[Wayners]

My Ford cuts power to cigarette socket after 30 mins.
My 16 year old Ford van has similar power cutting I've noticed after 30 mins.

As for phone charging flattening battery no chance. Probably need many phones charged one after another to flatten a car battery. If you want to know what's going on fit a Bluetooth battery monitor. 2 mins to fit and £25 well spent. Bm2 I use.

Reports crank voltage. If low battery needs replacing.
Charge state.
Overnight voltage drop ect

 

[flameport]

The battery is at least 5 years old but in seemingly good condition

Not any more, you now need a new one even if it was in good condition before.
Fully discharging a lead acid battery will cause irreversible damage.

Car batteries are not intended or designed for moderate continuous loads, and will run down far quicker than expected when used in that way.

 

[mointainwalker]

Not any more, you now need a new one even if it was in good condition before.
Fully discharging a lead acid battery will cause irreversible damage.

.

How will this damage now manifest itself and how can it be measured ?

 

[securespark]

We had a problem with a battery that went flat after listening to the radio for 15-20 minutes. We came to an arrangement with the dealer on a contribution towards a new one.

I got a Bosch S6 AGM battery that is still going strong 140,000 miles later

We can listen to the radio as much as we like without worrying the battery. The headlights were even left on one time for 30 minutes (this pesky model allows the headlights to be switched on without the key in the ACC position) and the car started no worries.

 

[securespark]

Not any more, you now need a new one even if it was in good condition before.
Fully discharging a lead acid battery will cause irreversible damage.

Car batteries are not intended or designed for moderate continuous loads, and will run down far quicker than expected when used in that way.

I once rescued the battery on my Skoda Octavia after it was fully discharged and left for 6 months.

It was winter and the battery was extremely cold and the voltage registered as less than 2V.

The manual of my CTEK charger stated that it would not run the reconditioning desulphation cycle below that voltage.

So I stood there with a hairdryer warming it up. Once above 2V, the charger kicked in and did its stuff.

Surprisingly, the battery was brought back from the dead and continued to do its job for the next few months until I sold the car.

 

[Burnerman]

Personally I’ve had many a completely discharged lead acid battery, and so long as it’s not been left that way for ages has recharged and behaved just fine.
John

 

[mointainwalker]

John, I agree with you. I certainly don't believe that flat battery = dead battery. It sounds like something a battery-producer would say.

 

[Avocet]

John, I agree with you. I certainly don't believe that flat battery = dead battery. It sounds like something a battery-producer would say.

Something to do with "sulphating up", I've heard. It's true that lead-acid batteries don't like being deeply discharged. You can get away with it a few times, but they don't hold their charge as well each time it happens. We convert cars at work, so we usually have hundreds of brand new ones lying around and we have strict instructions from the manufacturers to disconnect the batteries if they're going to be laid up for more than 2 weeks - or the manufacturer won't replace the battery under warranty.
My personal experience, is that you can run them completely flat about half a dozen times and then they're dead, but each time it happens they never really fully recover - even with a "reconditioning" cycle from one of those tricky CTEK chargers like Securespark has.
What kind (and age) of car is it anyway? As others have said, modern ones have fairly significant current drain if "awake" but not actually running. They tend to shut down their electrical systems in stages after a certain period of time, but might be prevented from doing so if they see a drain that they don't recognise.

 

[cdbe]

There's a chart somewhere on lead battery discharge cycles, something vaguely like thousands of cycles at 3%, hundreds at 50% and ten or twenty at 100%.