On 23/04/2021 13:43, Dave Plowman (News) wrote:
In article ,
williamwright wrote:
On 20/04/2021 20:02, Cliff Topp wrote:
All modern cars will have an amount of quiescent current draw to power
things like the alarm, the clock, the radio presets and so on when the
car is parked up and switched off. I've seen it written somewhere that
around 50mA can be considered 'normal'.

My question is - if the quiescent current draw is 50mA (0.05A), how do I
calculate voltage drop per hour?

For instance, if I park the car up at 10pm and the battery is showing
12.5V, with a 50mA draw overnight what will the voltage be at, say, 9am?

Couldn't the manufacturers fit a separate small battery dedicated to
supplying the quiescent items? One that would last maybe ten days. With
a user option to decide whether it should steal power from the main
battery when it became depleted?

Not too many would be keen on a car which still sort of starts, but has to
be taken to a garage to have all the things that rely on a memory reset?
Nor would it be a small battery. Up to 50 mA is a common quiescent drain.
Work out the size of battery needed to supply that for any length of time.

If you know the car is not going to be used for some time, disconnect the
battery. At least then you won't need to buy a new one when you eventually
want to use it.

The last Transit I owned had two lead acid batteries of equal size.
During cranking and running they were connected together. At other times
one was isolated from any gizzmos and so zero drain.

I guess that is one solution to the problem.