I had no problem downloading the software update. The cell service where I live is terrible. I solved that issue years ago by turning off cellular data in the Defender, adding a home Wifi router in the room over the garage and connecting the Defender to my home Wifi. Software now downloads perfectly via Wifi.

But I could not get the update to install in our 2021 due to insufficient battery charge, Tried about 5 times, including once after driving back from a 3 hour trip. Update still failed to load due to insufficient battery charge. My wife drives this Defender and with winter coming, I decided to replace the battery with a new one. Drove it home, tried the software install and it installed immediately. I guess after 3 years and 40K miles the battery was on the way out.

Of course the original battery passed some required charge level test at the dealer so it was not covered by warranty. I pleaded my case that if the battery is too weak to install software updates then it should be covered by warranty. Dealer said JLR makes the rules on what is covered under warranty. So for $500 my wife's Defender should both start and be able to install software updates for another 3 years and 40K miles.

 

Batteries are weak point it seems. Vehicle draws a lot of juice and charging system algorithm is very strange, I have voltage monitor plugged in (P300) and I can see that it doesn't charge sometimes, I could be driving and it stays at 12-12.2V, then it might go to 13.4 for few minutes or 14.5 and goes back to 12-12.2
Telematics goes to sleep after 3-4 days of inactivity.

 

I suspect that LR sets a very safe/conservative minimal battery voltage as being required before an update will go b/c if the battery is at a very borderline voltage and drops below the absolute minimum that the electronics need may result in an unexpected shutdown during an update which could result in a "bricked" ECU that would require a very involved service to recover from (corrupted boot loader and corrupted firmware image)....

Sort of like when you update a smartphone's OS it requires being plugged in if the battery is anywhere near 50% or lower.

A hassle, but probably not a bad thing to avoid bricked ECU's....

 

Makes perfect sense as a software update takes about 45 minutes to install. I can say from experience that if you have poor cell service where you live and you use the Defender's cellular data system to download the software update, bad things happen once you install it. (Such as seized power steering) Thankfully a "hard reset" by disconnecting the negative battery terminal for about 10 minutes solves that problem. Keep a 10mm wrench in your Defender at all times so you are prepared if the vehicle software suddenly creates some serious unexpected issue. Smaller electronic issues like sound only coming out of the right speakers are solved by a simple vehicle restart.