I've been using 2 fr2 decks with NiMh 4000mah NP-1 cells. In tandem with internal batteries - 2700ma nimh sanyo cells - It gives you 8hours easily, and I run with timecode. The Fr2 can use both external and internal seamlessly.
You don't have to spend a lot to get NP-1 form factor into your mix. You can get a 4000mah nimh battery for about $59.99 shipped on ebay:
http://cgi.ebay.com/12V-4A-Battery-for-Sony-NP-1-NP-1A-NP-1B-NP-1SB_W0QQitemZ140396418040QQcmdZViewItemQQptZBatteries_Chargers?hash=item20b04753f8You can get an idx single np-1 charger for around $10:
http://cgi.ebay.com/IDX-JSE-23-QUICK-CAMCODER-CHARGER-FOR-NiCd-BATTERY-NEW_W0QQitemZ380212860109QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item588673d4cdNo need to pay the $75 charge for np1>fr2 cable. Just do an ebay search for an np1 cable so you can cut the np1 cup from. A 4pin>np1 can be had for around @20, then contact sennheiser and request a dc cable for an HHB md500, which they sell for $14 (last time I bought one last year - fits FR2 power), you may want to get a couple.
Then just cut the 4pin end from the np1 cable, take the cup, match the polarity on the cables, solder them together (don't forget to put a piece of shrink wrap to cover the splices. and you have a reliable power supply dependable enough for "professional" work for a fraction of the price of alternatives.
Let's see, charger $10, Battery $60, cable $14, np1 cup $20.. for $104 you've got a very dependable power supply in a easy to use form factor. I've got 6 batteries in rotation and don't have anything but good results. I use idx lions v-mount for my camera, but the np1s cover all the audio power, and I have an adaptor where I can use two np1s on my camera if needed. Redundant? Not when successful results are your mission.
The fr2 portabrace has a pocket on the front that fits the above config well. If you use the multi pocket, you're going to have lots of room for cables, radio mics, whatever you wish.
Best,
John