Sena support suggested I post this on the forum. So, here it goes.
I bought a Sena 20S dual pack in Dec. 2014. The units I received were serial number 14XXXX units. Below is the battery life I experienced:
1. After a full charge, stand-by time was 20-25 hours with firmware version 1.2 and 30-35 hours with firmware version 1.3. This is with the units sitting on a table idle the whole time. ZERO talk time.
2. Two weeks after I fully charged them and put them back in the box, upon power up, they immediately reported "low battery" and powered off.
Because of the short stand-by battery life, I RMA'ed the dual pack and received two individual replacement units with 15XXXX serial numbers. The Sena reps were very responsive and replaced the units with zero hassle. Below is what I found with the replacement units:
1. After a full charge, stand-by time was 50-55 hours with firmware version 1.4. I didn't try any other versions. Again, this is with the units sitting on a table idle the whole time. ZERO talk time.
2. I recharged both units and put them back in the boxes with a Post-It dated "4/25/15". I powered them both up on 5/3/15 and they both immediately said "low battery" and powered off. So, the batteries drained in 8 days or less ***when powered off and in the box***.
Sena support said their R&D folks are saying stand-by battery life is now 2 days vs the 10 days originally advertised. Mainly because the mic is always on. I'm not sure if the mic is actually "always on" with firmware versions 1.3 and 1.4. My original units responded to "Hello Sena" with firmware version 1.2 no matter how long the units were in stand-by mode. But, the "Hello Sena" function stops working after 60 seconds in stand-by mode with versions 1.3 and 1.4. That might explain the 10 additional stand-by hours I got by going to 1.3 with my original units.
It was when I contacted Sena about the 8 days or less powered off and in the box battery life that they suggested I post it on the forum.