Twice in the last week, I got a message that the key couldn't be detected even though it was in my back pocket. I admit my behind may have gotten bigger over the winter but presumably not enough to block the signal from the key.
The car is only 8 months old which seems early to have to replace the battery.
I had a Bonneville that would go through 2 batteries a year while our Caravan is 14 years old and still has the original battery so it's possible that the Volvo is closer to the Bonneville than the Caravan.
What are people's experiences as far as how often a battery has to be replaced?

 

So is it the volvo's battery or the key's battery? If it is the volvo's then check and see how much the computer system drains the battery in standby, when active, and how much the alternator puts out. using some basic math using ohms law and a few more equations associated with batteries themselves you can find out if something in your car isn't adequate.

-Do you have a high amp-hour battery with a low internal resistance?
-Does your battery have enough Amp-Hours to run the electrical system idle for how long you let it sit?
-Does the alternator put out enough juice to charge the battery?
If so how long would it take to charge the battery with the chemistry of the battery, amp-hours, and internal resistance as factors.
-If the power runs off a battery how much does it store, what is the shelf life, and how much does the key pull.

Using this you can at least make it to where you replace the battery less often.

 

It's the battery for the key. It flashed the message a couple of times before I made the original post. Naturally, it hasn't done it again although I'm ready for it since I bought some new batteries for it that haven't been installed.

 

Alright well as an explanation of why they key may last a different time from different models of cars is that one key may be drawing less power than another.

Requirements of Remote Keyless Entry (RKE) Systems

Look over at "Power Conservation" on the page, and it may give you an idea on what else is in that tiny remote :3

depending on what is in the remote (backlight, lcd, live car updates, RF reciever, ect) If the key has a model number you might be able to find the power consumption (Ff you are lucky, nothing even comes with a schematic anymore sadly)

 

There must not be anything wrong with the battery for the key. I was washing the car out in the driveway today and had the key in my pocket. The car kept locking and unlocking so I put the key in the back of the garage, a good 45' away. Despite the distance, the locking and unlocking continued whenever I touched the car.

 

Now for that problem I don't have too much of a clue. It could be the receiver an the car has malnfuctioned, there could be a bad part on one of the boards. (Maybe bad transistor, logic gate , MCU or MPU.) I would suggest taking the battery from the remote and restart some computer systems (unplug battery for about 30 seconds to a minute)
This may fix the problem by restarting electronics or give an insight on if the remote is truely bad.others on the forum may be a bit more knowledgeable on the subject but that is what I would do personally in attempts to fix the problem.