Its only the paid for version that uses the bar code feature and a few more bells & whistles you also receive bar codes to stick on the battery's, the free version which is what I use as been said before you just enter details manually, I have taken a photograph of each battery with my mobile phone and this is stored in the RC Battery Watcher app along with all the details of each battery, dead easy to monitor and keep a check of your battery's quickly.
At the moment whilst flying under load you can use the ST16 display for voltage readout, or out in the field with battery removed as said before use a good multi meter to check the voltage but bare in mind it wont be under load so will read higher after standing for a while.