Chronomaster: 4 1/2 sec band over 5 years with new movement; what do I do now that batty is dead?

I can't help with advice on Chronomaster battery replacement.

I can help with an explanation for the disappearance of the 2 seconds.
They were caused by a failure to move the seconds hand. Once the rotor failed to move the first time, it was in the wrong position for the subsequent stepper pulse. The subsequent pulse failed to move it as well. Two seconds were lost.

The stepper motor needs a positive pulse to move the rotor to the North. And a negative pulse to move it South. And for that to work, the rotor needs to be in the proper position so that it can move North or South.

The new VHP's have this thing to pick up on those hick-ups and correct for them at a later stage.

Glad to see that your insistence on proper regulation has payed off. Eventually.

If you're doing it yourself, I've got one tip.

The last battery change, I made sure to properly grease the o-ring. That made all the difference.
Closing it was that much easier since you don't have to work against the friction.
And you're sure the rubber sits properly all the way round.

Lubricant meant for o-rings obviously.

You'll be surprised why you bothered with sending it to Japan in the first place.

Still love your inventive rate measuring technique.

Another thing learned.
Well done Sir!

You see those Breitling ads for their service. Clearly meant to intimidate.
No, you don't need an operating theater to change a battery. That is, unless you decide to swallow the battery.