Drain on Battery

[PDL COLORADO]

My battery is about 1 yr old & if I don't drive my '02 Sequoia for abt 2 days it will not start. I've had my local garage to check for a drain on it but they tell me there is none. I charge it up & it'll do the same, not start. So I have to carry a battery booster with me at all times.
Does anyone ever had. this problem or it this unique?
Thanks in advance for any answers as to why it may be happening. I've got about 275k miles on it, runs like a charm.

 

[Jgrauman]

things to check, voltage at the battery while the car is running, writw it down, voltage while it's not running, write it down. Let the truck sit for an hour and check again, write it down. Post up results