battery voltage

[malc1950]

Can anyone tell me if a 11.64 volts reading took off the jump points under the bonnet after the x has been stood for 20hrs is correct , the reason i am asking is my park heater runs for 40sec but doesnt fire up but if i  put a live wire to the park heater it will run and fire up ok , is my heater sensing that my battery is low ?
the battery is a bosch s4 and is only 6mth old , 

[X5Sport]

Way too low!  Sounds like you either have a battery issue or a parasitic power drain.  A good battery should read at least 12.4V even at the terminals.  Was the car asleep when you measured it?  If not you do need to test it with the car asleep.

Disconnected a good battery should show 12.6V, an 'open-circuit' battery when fully discharged will give 11.7V.  Connected you will see 12.2/12.4V give or take on a good one and maybe 10.5V on a bad one.  Anything less than 12V needs looking into.

Battery formula is 2.1V per cell, and a car battery has 6 cells hence 12.6V.

Your Webasto is almost certainly sensing the voltage is too low and so it will not fire-up.

Richard

[malc1950]

Hi Richard thanks for your help yet again, when you say asleep what do you mean, i turned off the alarm  opened the drivers door popped the bonnet shut the drivers door then connected my meter took the reading,
Cheers Malc

[X5Sport]

These cars computers 'wake up' into a sort of semi-operational state so that will cause a power loading.  If you look at the gearshifter you'll see a little orange LED glowing away.  If you leave the car alone for approx 16 mins that LED will go out and that means the car is 'asleep' so no large power drain.

Easiest way to do it is pop the bonnet then lock the car and (assuming no thieving git can get at it) go have a cup of tea.  Car should be nicely asleep when you come back.  Don't do anything other than check the LED is out (through a window) and do the voltage check again.

Sorted......

R

[malc1950]

Will give it a try later in the week when i have given it a good :drive: to fully charge the battery as its only been to the shops and back today,