3v wireless arduino and power consumption
The most efficient method (in term of power) is connecting primary batteries (not rechargeable) directly to the devices without any converter (buck/boost). You can use 3x1.5v primary battery (AA/AAA/whatever).

Li-ion, lead-acid, or other rechargeable batteries will self-discharge itself over time. 
Primary batteries, which aren't designed for recharging between manufacturing and use, have much lower self-discharge rates. You can see their discharge rates in this table: