My bike sat for awhile - perhaps just over a year - and then wouldn’t shift. No lights lit up on the SM-EW90 B unit. So I hooked up the SM-BCR2 internal battery charger. It perhaps showed an orange light while charging but this was never noticed. It was solid red for a week. Therefore, it was assumed that the battery pack was inoperable.

Rather than buying a complete unit 14430 replacement batteries were obtained and the battery pack was disassembled. Lo & behold the original batteries read 8V so perhaps the recharge on these 8 year old batteries was effective.

Seemingly obvious conclusions: The charger works, The battery wiring is connected as the battery charged and the (solid red) light is present.

Solution?: Reassemble the battery pack with either the new or old batteries and ride into the sunset.

Confusing issues: Why did the lights remain solid red. Will shifting actually now work? It must be stated that I don’t think shifting was tried before the battery pack was disassembled as the bike was chained up on a bike carrier in the garage. H’mm - that doesn’t make sense does it - it would still try to shift? Give me a break okay!

Your thoughts would be appreciated.
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Update. Many thanks to those that responded.
I thought this was a somewhat simple question but apparently it is quite complex.

First off I could find no association of DVM and Di2. Not saying it doesn't exist however.

Oh My! The reference to Better Shifting was an eye opener. This site is definitely geared to aspiring Tour de France riders but with a bit of clues and further digging I'm on a path to resolving this.

From one article on the great, great grandfather of components, the SM - EW90 B was this:
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What does the button do?

Depending on the battery and other components installed on your bike the junction box button behaviour changes. As described in the Di2 Beginner's guide, pressing the button for 0.5 seconds will turn the LED red and enter adjustment mode, allowing you to index the rear derailleur or adjust the front derailleur top limit.
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So it is presumed that the solid red light indicates that the unit was in adjustment mode. Also checking the compatibility listing the SM - EW90B is compatible with E-Tube which I had never heard of.

So the plan is to resolder the batteries into the battery pack and start over. I have downloaded the E-Tube app to my PC, will then have to get it to my phone, and then make whatever adjustments are needed. No doubt visiting Better Shifting will provide additional guidance. Many thanks to the site contributors for their contributions.