Most 7v garments will power for around 2-8 hours depending on heat setting selected and outside conditions.

Similarly, 5V gear usually lasts 2-8 hours as well, depending on heat settings and the environment in which it is used.

Popular primarily in socks, insoles, and gloves. 3.7V batteries tend to last a little longer even on high settings, usually around 4-8 hours.

Many jackets and vests can be powered for almost double this time with an extended-life battery, that are generally sold separately. 

Please see specific item pages for an indication of how long the batteries will last on a single charge.