In this case only one of these batteries would be flat. As soon as the ignition switch is turned the two batteries are connected. I dread to think the magnitude of current flow in the first few seconds.
Any flattened lead acid battery is going to be toast, or severely damaged.
Just experience of them.
At one time new batteries were dry stored. When you bought one, they'd add the acid. Not so now. Yet most would expect a new battery from Halfords etc to start their car right away, without charging. So they must have low self discharge. As not even Halfords will turn over their stock every couple of weeks.
Immobiliser? Radio memory? I'm sure the makers of expensive cars would do everything they could to reduce quiescent load. It's not a good advert if the car won't start after being left at an airport carpark while on holiday.
I really don't see an answer to it with modern cars. And I'm sure many very clever engineers have given it much thought.
How about more than 8760 hours? :)
A flea market purchase of a 2nd hand 12AH SLA I'd purchased for a fiver (after checking the voltage was at least above the 12v mark on a borrowed DMM) some five or six years ago. It was only when I retested the open circuit voltage with my own DMMs on my return from the flea market that I saw it was actually just below the 12v mark. I guess the cheap DMM I'd borrowed either wasn't blessed with a low battery indicator or else I'd simply not spotted whatever low battery warning symbol it may have possessed.
Even now, it still in good condition (12.87v rest voltage reading about a week or two after charging it up to 13.8v with my bench supply.
At that time, I did not have an SLA capable charger (or variable bench supply) to safely charge it so used a pair of 1.2Wpk solar panels hung out of the office window to take advantage of the summer sunshine. I checked the voltage daily until it just topped the 13.8v mark about ten to 14 days later. Checking the resting voltage the next and subsequent days showed a 12.85v reading which over the months, until the next summer solar charging season came around, dropped to 12.75v.
It did get used as a test voltage source for brief periods, often just to check it could still produce amps with very little sag using a 50W halogen headlamp capsule bulb (I wasn't planning on using it as a starter battery).
However, after two such summer charging seasons one winter's evening, I used it to jump start a 1.6l automatic whose battery had let me down outside of our local chippy. It was my own fault, I knew the battery was on its last legs but had still waited, engine off, with the parking lights on for SWMBI to return from the chippy just 10 or 15 minutes later, in spite of the street lighting allowing me to switch the lights off to avoid just such a situation. Being an automatic, bump starting just wasn't an option :(
I was rather surprised that a 2nd hand 12AH SLA purchased 2 1/2 years earlier and only ever charged up twice with a couple of 1.2Wpk solar panels could crank a 1.6l petrol engine into life so easily as it did some six months after it had last been charged up.
I learnt a valuable lesson that evening, namely to reduce the float charging voltage from the 2.133v per cell typically set by default with UPSes down to the less abusive 2.1v value if you want your very expensive "consumable" to last more than just a lousy two or three years (assuming few to no brief mains outages in that time and that the automated weekly battery test feature is also disabled).
I've regarded 13.0V on a 12V lead acid to be a maintenance charge.
Keeping a battery at a float charge level is said to enhance plate corrosion over leaving it to stand and charge periodically.
The point is that the engine management system/computer is still monitoring these functions and the computer programming has more inbuilt knowledge about the parameters being monitored than the average driver ever had.
My car now even has a message coming up on the dash if the fluid in the windscreen washer bottle is getting low and I'm guess I would get a similar message if the oil pressure was low or the engine was running over temperature.
All data could be stored in non-volatile memory requiring no power to maintain it when the cars ignition is turned off, or key/fob removed.
I guess the biggest user of standby power on a car is remote locking and the alarm.
You mean the manufacturer has designed in a feature designed to make you annoy the people behind you?
Andy
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It's a balancing act between the risk of sulphation at too low a voltage and premature corrosion at a high float charging voltage. 13.8v per six cell SLA (Gel or AGM) when sustained year in, year out, in a UPS application is IMO, way too high.
A more sensible choice of float charge voltage in this usage case would appear to be that 13.5v value often noted as the optimum operating voltage for mobile transceivers.
When I recommissioned my APC SmartUPS2000 with a cheap set of four 7AH alarm batteries almost three years ago to prove its compatibility with a cheap Lidl 1/1.2KW Parkside 'suitcase' inverter genset, I adjusted the float voltage down from the 55.2 originally set by APC to 54v (actually, the float charging circuit has a very soft voltage regulation and had crept up to 55.5v over the years since I'd last tweaked the relevant trimpot to set it bang on the 55.2v mark per the 13.8v standard, ignorant of this high voltage setting being the cause of early battery failure at that time).
Incidentally, APC specify an 18AH 48v battery pack for this UPS model which would cost somewhere in the region of 200 quid for an equivalent to the APC supplied battery pack which, afair, was priced in the region of
320 quid! Those 7AH alarm batteries will be hard pushed to give more than a minute's run time at the full 1500W loading so I'm giving serious consideration to investing in an 80 to 100AH 16 cell LFP battery pack to eliminate the overpriced short lived inefficient 'consumable' from the equation.The larger capacity UPSes tend to be designed to safely utilise an additional battery bank or three without overheating (they incorporate a cooling fan or two). That SmartUPS2000 of mine has one such thermostatically controlled fan but the ventilation owes too much of its design to aesthetics and not enough to function. I'll be cutting out the 'vent slots' (fan and intake) and fitting a wire finger guard on the intake - the fan doesn't really need one since it will give a warning sting to anyone foolish enough to try and shove their fingers into where they don't belong.
Anyhow, my point is that just last week, I decided to risk pressing the 'Test' button to see if there'd be any sign of deterioration of the battery pack's condition after three years of service. I'm happy to say only the top led in the column of five extinguished as per the initial commissioning tests so it looks like my decision to dial the float charging voltage 'back a notch' has actually paid off. :)
A lot of owner / users of APC UPS kit have for many years, noted and complained about the rather short service life of the batteries (typically just two to three years before they're totally shagged) but APC are not alone in defaulting to this common 13.8v per six cell SLA setting
- it's an "Industry Standard" that maximises the initial autonomy for a laughably marginal battery pack AH sizing.
I haven't seen any actual figures on this but I suspect reducing the float voltage down to 13.5v simply reduces the effective from brand new initial capacity by some 5 to 10 percent in exchange for a doubling, possibly even a tripling, of battery service life. Considering just how expensive these 'consumables' are to replenish, trading a few percent of autonomy for a considerably extended battery life is a no brainer choice in my view.
Most recent models of UPS can be adjusted to a lower float charge voltage setting by the user so it's an option that's worth investigating if you want to reduce the TCO of your UPS.
My experience over the past 5 or 6 years with that 2nd hand 12AH SLA suggests that the 13v maintainance figure you quoted will indeed protect an SLA against sulphation but, of course, the downside is that it won't be charged to its full capacity.
No great problem when its being stored and not expected to provide backup power at an instant's notice. It'll just need a boosting charge to
13.8 volts prior to being used or placed into service. If it's one of a bunch set aside to replenish a knackered UPS battery pack, the UPS will do this for you whether it's been set for 13.8 or 13.5 volts per 6 cell float voltage setting.Just one final observation (to get back on topic, sort of) SLI LA batteries (car batteries) are totally unsuited as a cheap alternative to SLAs for UPS service.
I found this out the hard way (I can be a slow learner at times) by going through TWO sets of NOS 36AH SLI batteries, each only surviving 6 to 8 months tops (and ONLY THEN did I recall a similar experience with a
4A 13.8v CB power supply floating a 48AH SLI battery some thirty years earlier which I'd simply shrugged off as a faulty battery at that time). Luckily, each of these sets of four car batteries had only cost me sixty quid - it could so easily have been a lot more expensive a lesson!
The fact is that people are being inconvenienced all the time by the quiescent drain preventing the car from starting. It shouldn't be beyond the wit of man to find a solution.
Bill
My tractor wasn't used for five months and it started instantly.
Bill
My 2009 Transit has that arrangement. It works well. The two batteries are squeezed in under the driver's seat.
Bill
I don't know why but I can tell you that that just doesn't happen. I don't know why. Maybe when the starter load is present there just isn't a rush of current between batteries.
Bill
If only - the first warning I had of a failing battery was the dash dials going haywire, and then the car came to a stop.
Rather less baffling is why the brake pad wear indicators hadn't come on after Halfords, for three consecutive years, reported low pad levels as an advisory at MOT time.
Albeit on a 5+ year old battery I once had a failure overnight. The previous day it started the car which had been sitting for 18 hours in temperatures below 0C. It started the car a couple of more times during the day. Previously there had been no indication of a failing battery and my daily commute was 30+ miles. On the morning of the failure the dash lights came on for a second or two and then dimmed to nothing, a turn of the key resulted in zilch. A morning on the charger did nothing.
A new battery restored everything to working order.
I once had disks and pads replaced by a local garage and years later when replacing the pads myself found that the low pad wires had not been connected - they had been neatly coiled up and cable tied safely out of the way.
<snip>
That was similar to when I was driving my mates AMG Merc to a dealers and it also came up with some form of 'Battery' fault before cutting out, before I could even turn round to take it back to his (about 2 miles away).
It had a big battery in the boot for running most things and a smaller one in the engine bay to start the engine.
'Apparently' it was the dual output alternator and put around £750 on the cost of the car before he could sell it. ;-(
Cheers, T i m
p.s. Got caught in some bad traffic the other day and the old Meriva started running on 3 cylinders and it threw up an engine management light (that reminds me, I should code read that and see what it was).
Using it again later (after it had cooled down) it seemed to behave ok but had also fixed the odometer backlight that had been out for about
6 months. ;-)
I had a pad on my Renault 20 wear down to the backing, which made for a gentle run home. There was a monitoring wire which fed an indicator, but because it was connected only to the pad on the easiest side to run the wire, it was also on the side of the caliper which wore least.
:-(
Chris
Unlikely to have a proper alarm.
I'm not really sure we need a sophisticated computer to tell you the windscreen washers are running low on fluid? After all many cars have told you about the fuel running low for quite a few years. ;-)
The answer is very simple. Either use the car before the battery goes flat, or charge the battery.
Cars run out of petrol too. No clever electronics can stop that - it involves some sense on the part of the driver.
Most brake pad warning systems show an error if the sensors aren't connected.
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