Digital SLR cameras don't normally get more than a few hours of battery life unless you carry spare batteries or use a battery grip. With this DIY battery mod, you can get up to nine hours.
DIY YouTube filmmaker Chris Winters takes a 10,000mAh external battery with a 9V output, a DC coupler, a hotshoe mounting plate and Velcro to keep his Canon T4i DSLR powered on for up to nine hours. Canon DSLRs have a small slot that allow the cable on a DC coupler to fit through the battery cover without a problem, but other DSLRs may not. Make sure to double check your camera before you get started. Click the source link for more details, including the list of recommended parts.
Increase Your DSLR Camera Battery Life To 9 Hours! [Chris Winter via Make]