On 20/04/2021 20:17, Chris Green wrote:
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?

At that sort of current it depends more on the battery's self discharge
characteristics than anything else.

In other words there's no simple answer, it depends on so many things:-

Ambient temperature
Battery condition (part or fully charged)
Battery capacity
Type of battery (wet cell, calcium, etc.)

And quite commonly (from experience of my own and neighbours), it'll
still be high enough to start after a fortnight, but likely not after 3
weeks.