4-bit MCU Availability - Again

Typical alkaline AAA battery is 860 to 1,200mAhr, but you might need two or three for the voltage. Rechargeable 18650 is typically 2200mAhr at 4V, but it might be too thick for remote.

This is nonsense - most low power MCUs today have a sleep mode (sometimes a deep sleep mode too) and wake up on input pin level change interrupt. Even on a cheap low power watch xtal at 32kHz the time lag for a button press is imperceptible to a human.

You can get various exotic chemistry batteries for low currents with a ~40+ year working life for specialist applications (at a price).

Zamboni piles are another technology that can almost last forever as long as you don't want them to do much work (well almost any). Mine is a just post WWII era night vision PSU and is still going strong. The limit of the work it can do is attract a piece of aluminium foil from one terminal to the other (until the metal work hardens and snaps off). A paupers version of this amazing physics demo running since 1840

Oh, you mean the higher priced parts...

Packaging? What packaging? At this quantity, they use chip on board. There's no programming. That's done at the mask level. This is why I was looking for people with specific experience with high volume, low cost devices.

Dude, just use a low power 8 bit MCU. No appreciable difference in power consumption.

Dude, that isn't the question.

Why do you expect that? They will probably tell you what you want to know although they might well quote a price that indicates rather clearly that they don't actually want your business.

If you were likely to be one of their customers at the volumes they operate then you would already know how to get in touch with them and have done it. Equally they would likely already know about you if you were operating at mass market volumes they consider sufficient.

You either have to knock on their door and convince them that you are looking at serious mass market volume and so worth them talking to you or simply do it some other way (8 bit MCU would be an obvious way).

OP is obviuously new to this market/design segment. His customer is buying 1M masked-rom chip for unknown 4-bit mcu from unknown supplier. They probably already have the market data, but none of the design data, and hiring a new designer for the job. There are two possibilities:

1. Previous designer died with covid and took everything to his grave.
2. New hot shot manager trying to upend existing department without touching any of the existing supply chain.

FWIW, TI recently announced a BT LE Arm Cortex-M0+ 32 bit CPU with price as low as $0.79 USD, CC2340. Standby current of < 700nA, 48MHz, and quite a number of peripherals and I/O. I'd imagine with an Arm architecture, it would go a long way to future-proofing the product. J

The details of the CPU part of an MCU is actually the least important part of a chip when considering "future proofing". It's much harder to deal with the peripherals and other I/O when changing chips, as they are very brand dependent.