A few weeks ago, I fitted a new battery in my Focus. I had noticed that it was turning over slowly in the mornings, and the lights were dimming and wipers slowing slightly. Since then I have seen a few unexpected improvements.

Firstly, the lights appear brighter. The starter spins quickly and the car always fires first time. My tickover seems smoother. When I switched the front screen heater on in the past, it made the lights dim, and turning them off made the stereo screen go black for a second. Since the new battery was fitted, the front screen heater has no effect on the lights or stereo. The stereo also seems to hang less.

I'm happy!

Sounds like your new battery serving you well then. Just like a new car now . 

Just replaced my battery too. Obviously the start up has improved. Not noticed any other improvements though. Will keep an eye on it!

Ok spent some time in the car over the last few days and found the following:

Improved lights, as per your post.

Improved idle and acceleration smoothness. Used to use the 97 RON petrol to get a smooth feeling car, but it's now feeling like that on the standard Tesco fuel.

My lights still dim when front heated switch is used, but maybe not as much as it used to dim.

Locking/unlocking the car used to sound laboured at times. ...not any more.

Loving the improved car...didn't think a new battery would affect all this!

You say your lights still dim.

is your alternator fully healthy

Jamie

4 hours ago, james_60 said:

You say your lights still dim.

is your alternator fully healthy

Jamie

Mine dim with the heated front screen.

The battery will act as a "capacitor" when in good nick, absorbing high voltage spikes and smoothing noise. This is why with a bad battery you will sometimes get horrendous noise from the radio, and other lights acting "flickery".

Similar happens when I used a relay without a back-emf resistor/diode on my old Corsa, when you shut the engine off (causing the relay to disconnect) it would send the central locking haywire. The electronics should not be damaged by high voltage spikes, but they may not tolerate it well at the time!

11 hours ago, james_60 said:

You say your lights still dim.

is your alternator fully healthy

Jamie

Yes it's fine. All the Ford cars I've had in the past do the same. It's only a slight dimming.

How do you know? have you measured your standing battery voltage (before starting in the morning), followed by measuring the voltage when the engine is running?  My lights barely dim when Start/Stop restarts the engine.  There's no effect when the electric screen is on either...

Errrr yes I did thanks. 😆