I have a 2019 Landrover Discovery and last week my wife got stuck at work, with the key fob not working. I took her the spare key and she got home. I replaced the battery and it worked fine until today - when she unlocked the car, got in and then it would not start and displayed ‘Low Battery, Please Start Engine’. However she could not start the engine, until I came over with spare key again.

For now, she is travelling with both keys - but any ideas would help

 

Low battery please start engine means the car battery is low. Not the key. I'd start with that - is it charging properly and holding its charge?

For the key fob they are sensitive to using a good battery. I bought a cheap pack of 10 a few years ago and they just didn't work properly - poor range, intermittent etc. I bought a more expensive 'normal priced' one as a replacement and it worked for several years. So you may also need a better key fob battery.

 

Are you sure the 'Low Battery, Please Start Engine" didn't mean the big 12V battery in the back, not the key battery?

 

Last thought. You can disconnect the main car battery for 30s and reconnect. That reboots the modules and might help reset. Although again you'll want to make sure car battery is well charged first.