I just went to the UK forum and right off the bat I saw many responses about battery drainage. I surmise that it is a given after cars age a bit.
wj

 

@Woo5ie , a TVR Chimaera 4.0 V8!! Fun!
@RichardS , I can't disagree with you, of course. Though we should educate some in recognizing that the quiescent drain on a 2006+ XK is rated at <35mA. That is 35 thousands of an amp! If the battery is 90Ah, 800 CCA... its going to take a lot longer than 30 days to drain!
In the workshop manual, section 4.2, it clearly states that batteries should be tested at 30 day intervals and charged at 90 day intervals, with the expectation and assumption that a sound battery is installed.
Not to mention that in some regions of the world, if you are parking on the street for 90 days... I'd be surprised if the wheels were still on it, which could negate the need for a battery, anyways.
And truly, there are periods within the calendar year that my vehicles sit for months on end, without issue.

So, back to 'what to do'. Fix the root issue or ignore it and play the charging game. We all have different approaches to this.

Cheers to all... global warming has afforded me a day of spring skiing ... in Feb! See ya!

 

We need to remember that the 90 Ah is a bit misleading. Even if the car is used regularly, the battery will only be around 80% charged. We shouldn't really allow discharge below 50% so we only have around 30% of total capacity to play with, which is about 30 Ah, which would be under a month at 35 mA. Also, if the car is only being used for short journeys of less than 10 miles then every trip is leaving the battery a little more discharged so a full recharge once a month would seem to be a sensible plan.

Richard

 

Running 12 volts over a fairly long cable is not such a good idea since the effects of voltage drop will be more marked (lower voltage and a higher current) than with either 115 or 240 volts where the voltage is high but the current is very low.

For a given resistance of cable, the voltage drop is proportional to the current squared, so it's beneficial to keep the current low. This is why the mains supply is high voltage cross-country; 115kV in the UK on the pylons (often). AC is used, incidentally, so the voltage can be easily adjusted using a transformer (which don't work on DC).

 

Sure, over a marked distance. An extra two meters isn't going to affect anything adversely. How long do you think most of the harness wires are in your car? Some can reach eight meters easy. No voltage problems in those, huh? I think you're being a bit captious.