Changed battery and now pendulum wont swing. Clock doesn't operate at all. All was fine until I changed the battery.

Check that the hands are tight and also that they are not touching. and jamming. Remove the battery and replace it. Some have a lever to give it a jolt to get moving.

https://www.google.com/search?q=Infinity+group+Pendulum+Wall+Clock

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If your wall clock is running but the pendulum is not swinging, it may be due to a few potential issues with the pendulum mechanism. Here are some steps you can take to repair the pendulum mechanism:

1. Check the suspension spring: The suspension spring is a thin strip of metal that hangs down from the top of the clock and holds the pendulum in place. Check to see if the suspension spring is properly attached to the clock and if it is straight. If it is bent or damaged, it may need to be replaced.
2. Check the pendulum leader: The pendulum leader is the part of the clock that connects the pendulum to the clock's movement. Make sure that the pendulum leader is properly attached to the clock and that it is not bent or damaged.
3. Check the escapement: The escapement is the part of the clock that controls the swing of the pendulum. Make sure that the escapement is properly lubricated and that it is not damaged or jammed. If it is damaged or worn, it may need to be replaced.
4. Check the beat setting: The beat setting is the adjustment that ensures that the pendulum swings evenly. Make sure that the beat setting is properly adjusted by moving the pendulum to the left or right until it swings evenly.
5. Check the weights: If your clock has weights, make sure that they are properly attached and that they are not obstructed or damaged.

If you've tried these steps and the pendulum still isn't swinging, it may be best to contact a professional clock repair technician for further assistance. They will have the expertise and tools needed to properly diagnose and repair any issues with your clock's pendulum mechanism.

It is a handsome longcase clock and rather elaborate - it would be disappointing to discover the weights and pendulum are merely decorative.

I have only encountered one similar clock and it had one battery to keep the pendulum swinging and another to power the clock. The battery had to be fairly fresh or the pendulum stopped swinging. The clock also had to be level or the pendulum stopped.

If you took the picture when the pendulum was stationary, the clock appears not to be standing vertically. It is important they stand vertically in both planes to the nth degree.
There is also a fable about a clock never being happy standing next to or hanging on an exterior wall, sometimes not such a fable...

I don't think the pendulum is the problem. I suggest you should level the clock (considering the shape of the case a plumbline would be best), fit a new battery and give the pendulum a swing - if it doesn't keep swinging, there is probably a fault with the motor.

probably find that the clock has it's own aa battery
the pendulum has it's own aa battery and the chimes have 2 aa batteries

Replace the clock movement from a source like eBay.

Give it a push sideways to get it started.

It sounds like you may need to repair the movement.
http://usedclockparts.com/14-clocks/clock-videos/126-quartz-battery-operated-clock-movement-repair

Clock may either need to be decked out from the wall at the top, or pushed all the way up against the wall. These clocks have inexpensive quartz movements that aren't of the highest quality. If the clock is more than a few years old, it may be that the electromagnet that impulses the pendulum back and forth has just expired. You might try Clockit.com, or maybe Timesavers.com to find a replacement movement. Hope this helps, Good Luck

Good details! Go to Timesavers.com
You can find a replacement pendulum unit there. Your pendulum mechanism probably has a bad coil. The coil is extremely difficult to repair.

I have a clock with a pendulum and it has two batteries, one for the clock and one for the pendulum.

Perhaps your is the same?