"Dave Liquorice" wrote in message
ll.co.uk...
On Sat, 10 Oct 2009 08:44:32 +0100, Dave Plowman (News) wrote:

According to an expert on another group the average lead acid car
battery loses 60% of its charge per month.

Naw, thats worse than NiCd!...

I'm only quoting this FWIW as it's not my experience. I have a clever
electronic battery tester which works out the actual capacity and that
shows nearer 20% per month.

I'd say even that is high, no doubt that also includes the energy
taken by the tester. Lead acid batteries have a very low self
discharge, Battery University say 40% per year (3%/month average):

http://www.batteryuniversity.com/partone-6.htm

Of course if the battery is left connected in a modern car, the
quiescent drain may well flatten it in less than a month.

Agreed, modern cars have a "deep sleep" mode that they can be put
into. The makers use this when brand new cars are spending weeks on a
boat traveling the world or parked up on disused airfields waiting to
be sold.


I've not heard of this. But not saying it doesn't happen. My experience is
that new batteries have electrodes of high purity, such that batteries have
a very low rate of self discharge. They may well retain their charge over
an extended time. One issue when fitted to a car is that some of the car's
gadgets do consume a small current.

I had believed that batteries were generally shipped dry, with the
electrodes in their formed state, where on importation or before sale, were
topped up with the correct strength of sulphuric acid. A dry battery will
quite literally last years on the shelf. Again I could be wrong.