how does the 661 work with internal nimh rechargables? I've been REALLY impressed with the power/capacity of maha NiMh aa batteries, a pair will run my m10 for well over 12 hours!
My 2,300mah Energizer NIMH AAs would power my old M10's for around 18-20 hours, which was PERFECT for ONE M10 and day of recording at a big festie! Man, I do miss my old and lil M10's. A pair of lithium AAs would probably power the M10 for over 30 hours. INSANE!
Anyway, to the OP, I realize that you said you don't want to use ANY AAs, but I would power the VMS5u with some AAs internally, and then run a SINGLE battery like the ones linked by others above, to power the Mytek & 661 combo
That would probably be the easiest and most stress free way to go if you'll be recording for a long time! Ive never run a VMS5u, but I realize that it takes 6xAAs. My VMS02IB takes 8xAAs, and it gets like 18 hours with some of my fully charged 2,300mah Energizer AAs, so I'm guessing that the VMS5u gets like 12 hours at least with some AAs internally! That should be long enough for you!
So yeah, run some AAs inside of the VMS5u, and a 12v/5v combo USB style battery and that way, you'll only have to deal with ONE external battery! I also highly recommend the 9.6v NIMH RC batts for your VMS5u, if it has the same voltage range as my 02IB does, and If you have a nice charger for them! I have a Tenergy TB6B Charger[$50], which charges ANYTHING[Lithium/SLA/NIMH/NICD/etc] and is the only charger I REALLY need, even though I have dedicated AA/AAA and Vape battery chargers too! Love it and it has a real-time readout about the battery being maintained
I am not crazy about the Tamiya connectors though that come stock on most RC batts, but I am eventually going to upgrade those crappy Tamiya connectors with some SOLID locking connectors like Mini-XLRs, which is pretty easy to do if you're handy at all with a soldering iron