A question for our electrical gurus. My battery went flat today down to 7 vols and a relay kept dropping in and out causing the panel LCD to flicker. I lost the clock and presumably the ECU memory setting.

I think it was because I left the ignition on for a couple of hours, stupid I know.

This set me thinking,

That was quite quick to run down the battery in 2 to 3 hours.

The relay dropping in and out could not be doing any good, fortunately I was there after the 3 hours and stopped it by putting on my battery charger.

If I go on holiday and leave my car for a couple of weeks, should I disconnect the battery especially if I leave it in an airport for example? If this relay continues indefinite what will happen?

I was also surprised that after only 10min on the battery charger I was able to start the car. I suspected the battery and had a load check done which was OK.

A 1.4 engine has typically a 36Ahr battery at the 10 hour rate so a battery a few years old (of reduced capacity) would discharge in the way you indicated with a discharge current of 5-10A; feasible if you had the doors open or other loads such as the heater fan on and certainly if the mirror heaters were switched on.

Don't confuse battery capacity and maximum current for starting. They are related but starting current is more to do with the internal resistance of the cells, cell connectors and posts. Modern cars using alternators have batteries with high "cranking" rating [low internal resistance] and less Ahr capacity than of old.

The low current taken by the alarm/immobiliser, clock etc will not discharge your battery during the two week holiday as long as it is less than say 4 years old and longer for some. Some airports provide a starting service if it does goes flat.

Leave your battery connected so everything is kept alive (alarm especially). The relay is off when the ignition is off.

The battery is only 18 month old. I realise there is a cranking current and an Amp/hour rating, don't know the A/h rating of my battery, presumably it is as you say. I do have a clip on Amp meter which may be interesting to see what current it takes with the ignition on. nothing else was switched on at the time only the ignition.

It is a bit disconcerting to hear the relay cycling if the battery goes flat because this will happen to all Scoda's

Edited 25 August, 200916 yr by Roker

The relay is clicking on and off because the battery is over discharged - you said 7V.

As the relay takes current it switches on additional loads through it's switch contacts. The extra load then reduces the battery voltage further, down below the voltage at which the relay can stay on. The extra load is then removed after the contacts open and the voltage rises again. The pattern then repeats.

It is not a Skoda problem but an over discharged battery problem that may happen with any make of car.

If you have a d.c. clip-on ammeter, I would be interested in knowing what current is drawn.

I have just checked my car with the ignition on but without the glowplugs (you don't have any) it is 10A with the driver's door open and 8.2A with it shut so it is not surprising that your battery was flat after 2-3 hours.

There will have been some loss of capacity/life in the battery but as it was recharged quickly it will not be immediately obvious.

For any one that is interested. The current with the ignition turned on and everything else off is 5.7 Amp, with the ignition key out it is negligable at 0.01 Amp

the battery is 55 A/hr asumming it is less now because it is not a new battery. 55 ÷ 5.7 would run the battery down in a few hours.

The relay I am told is a voltage protection relay, which drops out on low voltage to protect the ECU (still don't like the cycling on/off)