Hello! Seeing as there is unfortunately no official solution for this, I'd like to ask what people have found to be best for easily/quickly charging, powering for a decent amount of time, and somewhat more importantly, safest for the recorder? Cheers!
I've used batteries made to power portable DVD players with my FR2. They work quite well and usually come with cable and adapter tips that fit the DC jack on the FR2. If not, you can find cables/tips at Radio Shack (or a comparable place) that will fit. It's been a while since I've used it, but I think I was getting 6+ hours off of a battery. Though, it might be better/easier just to get rechargeable AA batteries.
Here is an example of the type of battery I'm talking about (I've never used this specific model):
These guys do a battery pack http://solidstatesound.co.uk/fostex_fr2.htm
Not sure if you're in the UK or not but they might ship out?
I went to a remote control shop, bought two Tamiya 4300MAH batteries, and then got the shop owner to wire a parallel series cable togheter (like a Y splitter for batteries).
I don't charge in parallel, but when they are both fully charged separately, the will last for hours and hours. Works a treat.
A production mixer buddy of mine, back in the day when he started with an FR2 before going the way of a 788T, had is FR2 modified with a Hirose connector, in which he was then able to power it via NP1 batteries... these batteries are a brick a smidge smaller than a DVD case, but I'm told a single NP1 charge can go for days on end even with a recorder/mic running on standby (if not actively recording).
Your question is a good one to ask production mixers for their opinions, since in my experience they tend to be the most vigilant and "in the know" about how to stretch every single last drip of portable power they can to maintain the most uptime possible.