battery drain
 

having had problems with the battery draining when my D2 A8 was left standing for any length of time I checked the parasitic drain in the approved manner using a 1ohm 10watt resistor
it seems to be running at about 100mA
is that about normal for an A8 ? seems a bit on the high side to me

How does one check with a resistor, would love to know your technique

for comparison, my current D2 S8 draws around 0.18A (using Maplin clamp Amp meter) and has very few options, my previous D2 S8 drew over 0.2A

A simple calculation, 0.1A over 24 hours is 2.4Ah capacity per day
If you have the standard 85Ah battery, and if it was fully charged, at your current rate of discharge it would take roughly 18 days to drain down to 50%
If your reading is correct, I suspect your battery is either discharged, or heavily sulfated and wont hold a charge.

Check your open circuit battery voltage. When fully charged, check its open circuit voltage, then leave disconnected for 24 hours and check voltage again, or connect a 12V bulb or something that draws a decent current accross the battery briefly, leave to rest for 10mins and check the voltage again. If the open circuit voltage after standing or brief load drops significantly from fully charged voltage, lets say from 12.7V to 12.3V or less, then your battery is heavily sulfated and hasn't got much of the original capacity remaining. On the web there are articles which reference open circuit voltage to state of charge. From memory, 12.0V or below is pretty much fully discharged.

well , as your's is running at about 180mA seems mine isn't bad at all !
my battery is excellent but , as you know know , this 100mA drain will half discharge a standard battery in a month [ pretty common when I am away in my motorhome ] at which point the voltage will be down to maybe 12.3 volts and there isn't enough to start the engine if it is at all cold

delboy , presuming you have a meter and a couple of spare crocodile clips £1 at maplin's will produce what you need


https://www.youtube.com/watch?v=B__DqK90IIc

Ah, yes, a month will kill it.
According to the interweb, if you leave your lead-acid battery sitting below 50% charge state for a significant lenght of time, it will form lead crystals reducing its capacity.
So going by the web, I doubt your battery is in a excellent state if you left it drain to zero for a month.
Also depends on the electical systems of the car, on my current S8 the old 110Ah battery could still just about start the car even when it was fully drained down to 11.9V

I have not measured drain current on mine but I have 6 years old 88Ah 730CCA battery which according to conductance tester have 61% capacity left and 630CCA and it recommends to replace the battery. If car is left alone for 2 weeks battery voltage will drop from 12.6V to 12.2V but it does start just fine at this voltage. I have had battery to drop to 11.5V in the past and it still started car but engine was barely turning over.

My 110Ah Varta must have been truly toasted by the previous owner, only 2 years old according to purchase receipt, and it was draining to 12.2V after sitting for just 5 days after being fully charged. How easy/cheap is it to do a conductance test, just out of curiosity?

There are several different testers on the market starting from about £20 to several hundred depending where you buy and what brand you want. I have a one like this for about £30: http://www.aliexpress.com/item/2015-...272748629.html

It's not the cheapest but it can test battery either in or out of the car and also can test starting and charging on the car. Only drawback is that it is for batteries up to 800CCA, you can still test higher CCA batteries just by setting it to 800 but results will be somewhat limited and a bit off. There are testers capable of more CCA but more expensive.

Thanks +++
£20 is very reasonable, I might get that one. The 110Ah is no longer in the car, I'm just curious what capacity is left on it.
Although I just realised I could charge it up to full and put a small load on it and record the capacity drained over a period of time. I have one of those RC multi meters which records mAh taken out of a battery, Ams and Volts.

not sure it is of great value to measure how much life is left in the battery , it either works for you or it doesn't , its a consumable product after all ; being a motorhomer [ with 3 batteries ] I am always watching them [ built in meter ]

on the A8 [ 95Ah 800CCA ] I have just fully charged the battery then disconnected the earth immediately and left for 2 days ; as you will all know a brand new battery will give you 12.7 volts but that doesn't last for more than a couple of weeks before it drops to something like 12.6 ; mine is reading 12.63 so I am more than happy with the amount of life remaining

with regard to drain tests I first used a clamp meter , but frankly I wasn't satisfied that it was sensitive enough which is why I sported £1 and made the resistor test lead

frankly goran I suspect you have had something draining the battery on both your cars ...searching around I found that top end mercs are renowned for a heavy draw but that 60mA would be pretty normal on one of those...I shall carry on looking , maybe you should sport £1 and do the same !

incidentally , if you give your 110 battery a long slow charge then leave it for a couple of days what sort of voltage do you get ...anything around 12.5v and it has a lot of life in it if you can reduce the draw !