My back from vacation results of battery usage with my Olympus E-M1. I took 3 batteries + 2 chargers. And I needed them all. The batteries lasted about 4 hours of heavy use in my E-M1. Battery-1 went empty at about 11am, battery 2 went empty at about 4pm, then I was on my last battery (#3). Based on usage, battery-3 would go empty at about 8 or 9pm. I was hoping that battery-3 would not go empty on me, and luckily it did not. A LONG HEAVY day, without access to AC power, may call for 4 batteries. As soon as I got to the hotel, I started charging 2 batteries at the same time. Then charging battery-3 as soon as one of the 2 finished. The trains thankfully had 110vAC so that I could plug my charger in, and charge as soon as I pulled the empty battery out. The E-M1 battery does not rapid charge, so it takes a few hours to charge up. If I start the charge as soon as I got to the hotel, it would be charged before bed time, and I could put #3 into the charger over-night. Then I would start the day with 3 fully charged batteries. This battery usage was quite a change for me, where my DSLR could easily go a full day (or two) on one battery.