USE A CAR BATTERY! Not your car. Lol.
All that walmart power box thing is going to do is fail in less than one season. Nobody uses them outdoors, for a reason. The first time it rains, or some kid trips over your cord and ninja kicks your setup halfway across the field, you'll be sorry.
Go to your local air field. See what they use.
Get a waterproof fully potted 12v/120v/6amp Guest Marine charger for maintaing the car battery. I use two G31a1000 truck batteries, with removable cap to check fluid levels.
Its not uncommon to chew through an entire g31 in one day. Charging 1/8th scale and airplane batteries.
I use this setup outdoors. If the outdoor track offers power, I still us it. Just plug in the charger to keep the truck battery topped off. I'll be perfectly charged, even when some momo trips the breaker with his compressor.
You can use a smaller battery with 1/10th scale. But I dont, because most dont have popable caps to check fluid levels and keep the battery safe around smokers and kids.
Usually just my cheapo Turnigy charger. But if weather's perfectly nice, I'll get out my Junsi Duo.
As for the weight thing..It's one less rep at the gym each week. Non-issue. Get two batteries, one for each arm, to be easier to carry. Do a few curls on the way to wherever you're marching to.
99% of the time, I charge on my trucks tailgate. Can 4wheel right up to most tracks. Wrench on a pit table nearby. So no carrying anything all season long.