I have recently Put together a DIY battery solution myself, it rivals the PB-70( 4 hours of straight continuous recording + the internal battery ) but it only cost around 80$.....( Ebay)
You could build around 4 for the same price as 1 PB-70.
And because it DIY, you have the ability to add as much input and outputs as you would like for your accessories( Mics, Monitor, etc....) Also uses a standard Laptop battery charger.