The OnePlus 3 includes a non-removable 3,000 mAh (11.55 Wh at 3.85 V) lithium-ion battery. This is a 300 mAh, or nine percent, reduction in capacity compared to the OnePlus 2, so it seems OnePlus is banking on energy efficiency improvements to provide similar or better battery life in the OnePlus 3. One thing to note here is that the OnePlus 3 is a lot slimmer than the OnePlus 2 for only a small reduction in battery life; the improved design hasn’t had a huge effect on battery capacity.
The biggest issue I have with battery life here is Wi-Fi browsing performance, which is very average. However the reduction in battery size hasn't affected battery life, with the OnePlus 3 lasting essentially just as long as the OnePlus 2.
For charging, the OnePlus 3 crushes the competition with its "Dash" charger. The unfortunate thing here is that to reap the benefits of fast charging, you must use the included charging brick and cable. Wider fast charging support, particularly using different cables, would be appreciated.