Battery Calibration Qs

No one can really answer your questions other than whoever provided those instructions.

Having replaced batteries in similarly aged Macs myself, I find any proposed "calibration" instructions to be dubious at best. Your model MBA's power adapter LED state accurately indicates whether it's charging or not, so leaving it connected for any arbitrary amount of time after it is fully charged — whether it's 2 hours or 24 hours — seems pointless.

2. Does anyone know about how long a fully charged battery will take to discharge to shutdown with the settings above if just left to sit? What if I just had iTunes start playing all 6,500 songs in my library (iTunes says it would take about 14 days, 5 hours), how much would that speed up the discharging?

You can determine for yourself how much power is being drawn by examining System Information > Power. If it is your objective to maximize (or minimize) power consumption you can see for yourself which apps draw the most power by using Activity Monitor.

It looks like it took about 1.75 hours to go from 99% charged to 80% so I forecast it will be at least another 8 - 9 hours before the MBA shuts down and I can then put it back on the charger.

Oh and one more thing... the dubious purpose of such "calibration" instructions is to more accurately assess the battery's state of charge so that macOS can render the "percentage" figure with a degree of accuracy. Until you have used the battery for a while, any attempt to extrapolate its run time from the alleged 20% discharge will be inaccurate.

Just use the battery and don't obsess about it. Maybe in another ten years you will want to replace it again.

Look at the current consumption, not the charge remaining. It's the value shown as Amperage (mA) and will be negative when the battery is supplying power (*). That's a reliable value that you can use to extrapolate remaining run time from its full charge capacity displayed as mAH. It also changes with whatever the Mac was doing when that screen was displayed, so you have to hit Refresh for it to update.

The battery percentage shown in the Menu Bar is 55%,

Full charge capacity ÷ current charge state is where it gets that information. The full charge capacity will vary over time (it might go up or down but the long term trend is down).

While it's charging, Amperage (mA) will be zero.

(*) newer Macs don't show that information. I suspect Apple either doesn't want us to know or that we wouldn't understand it.

Welcome to the Apple Support Communities.

I strongly recommend you contact Apple Support for battery service: Get Support. No third party battery has nearly the same quality as an Apple battery, and using the battery can result in safety issues.

Please refer to this from Apple Support:

Beware of counterfeit parts

Some counterfeit and third party power adapters and batteries may not be designed properly and could result in safety issues. To ensure you receive a genuine Apple battery during a battery replacement, we recommend visiting an Apple Store or Apple Authorized Service Provider. If you need a replacement adapter to charge your Apple device, we recommend getting an Apple power adapter.

Also non-genuine replacement displays may have compromised visual quality and may fail to work correctly. Apple-certified screen repairs are performed by trusted experts who use genuine Apple parts.

Jack

Some other thoughts about calibration, may need to be reconsidered.

In the step(s) you take to cycle the battery from charge/discharge/charge

to make the battery near flat in this process, you may choose to use iTunes

player or Internet Radio; forget libraries of saved music. Run the animated

screen, too. That uses some energy on battery; with a full screen light show.

Takes a few hours, if display is not dimmed and other power savers, shut off.

When charging as needed, not calibration: Be sure to note battery's status

in System profile or charge status in battery menu. That's a known factor

if the numbers do not match. - Some have & use third party battery apps;

those do OK. "Coconut battery" has a usefulness. When the specs show in

the system report, that's a fair gauge. At times, the last 4% or so, is slow to

reach when recharging. It may take 10 min, or maybe an hour.

When not using the portable Mac for few months, better to store it w/

near 50% capacity; check on it over a few weeks, to see what it shows.

A few times a year, maybe, I might run a calibration cycle to look into

battery's state or condition; but keep in mind: too much can endanger

the battery health. And since I've four Macs (2 portables) varying use

and messing with batteries, is not a preoccupation. To forget MacBook

is an easy oversight. There's pesky issues with iPhone. I curb the urge

to break that s@#$%ker Ask me why I have it? Still prefer landlines!

Keep in mind low 'charge cycle' count makes a difference; do not overuse

the calibration effort. A few times after you replace a battery? Maybe OK.

NewerTech & OWC have re-calibration page, for their brand & 'other' cells.

If after a few months you see in system reports a battery appears not-fully

charged; then charge it a little longer. You need not 'calibrate' to correct it.

Both my portable Macs have 'newertech' DIY replacement cells. Not the first.