I'll take one more try.....there are no replacement batteries for Omicron V1 nor the very similar O-phos. The battery is built in and the user can't open it or service it once inside, it's a job for the shop (or you scrap the unit as it's done it's service, the most expensive part being spent and the rest worn). Only Omicron V2 and Persei offer replacement batteries in this line.
Original (V1) kits came with two units since one could die on you in use (no battery warning). V2 came with a replacement battery for this use (put the fresh battery in and press on). O-phos comes with the understanding that you'll plug it into a USB port (or wall outlet) and use the 'pass through' function (really only a real time recharger built in) for that use. If you want to be out and about (away from power) and wish that backup you should buy a second O-phos (they're cheap enough, really) and carry both, or a V2 with a spare? Or you can just keep track of you charge status.
I wouldn't count on any estimates of battery life, they are at best estimates. A few deep discharges, or some overheating and that number drops fast. The batteries in these units are pretty good, but they are no more magic than the ones in your cell phone or laptop....where much more money is at stake to get the best technology available. They should go many years of normal service (say once a week charging), heavy use or abuse will cut that shorter. In that time, they will no doubt vape up many hundreds of dollars of oil. They should get weaker at the end, not suddenly go dark.
OF