Does your keyless go take a few seconds longer to recognize you when you haven't used your car for a few days? It could be just me but it seems that the door and trunk unlock instantly if I am in and out of the car a lot, but it takes a few seconds if I haven't used it for a few days.

Yeah it seems like it here.
When we got back from Hawaii, the car seemed to be on a lunch break or something when we tried to get in it for the first time.

Keyless go (as other "battery consumers") goes "offline" after some time to save (consumer)battery life. Usually takes a couple of days in my case.

Do you know if there is a way to make that time shorter? I repeated find that after a few days the battery is already almost dead because of no driving

No, I think this is burried deep in the software of the car.

Might your battery be up for replacement? A 'few days' seems too short to me.
Come to think of it, the SL55 has 2 batteries, one for the power hungry 'consumers' and one to start the car. The latter should always have juice, unless someone hooked something to it that shouldn't have been (alarm?). Or maybe that one is up for replacement?

The car always starts, that's not the deal, it's the issue of the consumers battery pretty much always being dead.

I'll see if I can get it checked, right now the car is in the shop getting a new alternator (and possibly, a hundred other items).

I'm glad my dad has more patience than I do, otherwise this car would have been on sale yesterday. I don't like being put on the side of the road for no reason

Are you saying that the battery in the key fob goes off line? That would make sense to me.

In the end the only thing still online is the key-fob

The sensors in the car stop 'asking' for nearby keys to respond. That's why it takes a while.

If the batteries in the keys went off after a while, how would they know to come back on?