Yep the ELT g-swithc activates on an acceleration of 3.5 ft/s, and they have a battery life of only 30 days upon activation.
A tad pedantic yes .. but ft/s is a velocity. Ft/s/s is an acceleration. I'm not sure where the 3.5 value comes from (a pedant would label it as -3.5) but it seems awfully small to me. At that rate it would take some 28.5 seconds to decelerate from 100 ft/s to a complete stop. That would mean the ELT would activate upon normal braking after a landing.
(Edit to correct time to stop)