My standard setup for fest recharging, since I almost always primitive camp off in the woods, is a deep cycle marine battery. I use it to recharge everything I have that is rechargeable. Sometimes it also runs a portable stereo system for playing back recordings at camp.
I don't use an AC converter though, everything runs straight 12VDC. That works for charging 9V DVD batteries directly, my phone, and powers my Maha NiMH chargers for the 9.6Vs, AAs & AAA's.
I made an 'octopus' with battery charger clamps on the battery terminal side , a car-type blade-fuse for safety, and 6 cigarette lighter sockets on the other end into which all the charging stuff plugs into to juice multiple things at once.
If your AC powered gear or chargers uses a 'wall wart' transformer or switching supply in the power cable, check the power labels on the gear or transformer, it may run directly off 12VDC and you can eliminate both the wart and the complications of having to use a converter.
A converter will work fine too, just not quite as efficient, and you need to remember to turn the converter itself off to keep from running the battery down.
Not sure about the specifics of what input charge power the M148 or your lithium pack needs.
The other nice thing is that the marine battery can also act as an emergency jump-start source in case you're the last vehicle to split on a lazy Monday after the fest, all tired and content, packed and ready to go, then turn the key and it just goes 'click'.