The vamo has a built in battery checker i got the v2, if it works the same as mine hold down the left button it'll tell how many volts are left should read around 4.1-4.2v for freshly a charged battery. Multimeter wil read around the 3.7-3.9v mark though with my setup i get the higher numbers.
Silly question how are you gauging battery life by vapour production or is the vamo flashing low v at you?
True it's just op's comment about a safe voltage and wattage they only run one or the other if he's in watts mode and it's reading 3 volts i'd say fecked battery but. To me something don't sound right with how the vamo's being used.
I've found that 3volts no matter what atty i use is rubbish no flavour or vapour i'll edit my previous post to try and be a bit clearer.