Lost iPhone sending a location after a week being off

I know iPhones will send locations even if the battery is dead

If the battery is really most sincerely dead, the iPhone is not going to send a signal out. So, if the phone is updating on it's location, the battery is not yet completely dead.

There is a difference between a "last known location" or "current location". If Find My is showing "last known location" that's what it is. The phone may or may not still be at that location. No way to know on that.

If "last known location" is not displayed, then the phone is sending information about it's current location at the time.

Unfortunately, there is nothing that you can do as far as telling the phone to tell you where it might be located at any given time.

Any idea why it stopped updating its location for a week then?

The phone cannot connect to cellular or Wi-Fi because of it's current battery condition, but it can still send out an intermittent Bluetooth signal with information about its location. If there is another Apple iPhone, iPad or computer in close proximity to the lost phone....at the time....it can pick up that signal and forward it on to the Internet. This is the same way that an AirTag works.

So, the lost phone might be sending out a signal every 3-4 hours or so, but if there is not another Apple device in close proximity to pick up the signal at the time, the information about the location of the phone cannot be forwarded.

As the battery condition further worsens, the phone does not send out a Bluetooth signal as often, so it might be sending out a signal only a few times a day at this point.

So, there are number of things that all must happen and work together to provide you with a current update on the location of the phone.

And about the 'pending' message when trying to play a sound, can I assume it's not connected to wifi?

The phone is not connected to either cellular or Wi-Fi if the battery has run down. Not sure how playing a sound would help, unless you are looking for the phone in your home or another spot where you know you misplaced the phone. There may also not be enough battery power to play a sound. The Bluetooth signal requires much less power from the battery.