LiPo batterys are very good, i have used them at model aircraft and now use one of the packs to my smaller rigs, FT817 can operate severat hours with my pac. It is on 11,1 Volt and 40A max. Fills my hand, not much bigger than my computer mouse.
WARNING: This kind of battery is sensitive for mecanic shock or damage, it can start to go to fire, not so nice if you are alone in dry forest or indoors.
Why that? The chemical substance is oxygene sensitive so if the package cracks or it is beeing any hole on it it get in oxygene and it will selfcombustive, Also the package must not be mounted in a tight closed area it must be place enougth to "breath", it expands if it is used hard and getting hot. You can surely find much more of this info at electrical model aircrafts homepages.
