I recently bought a 7.8Ahr Minimax lipo battery pack from Home Depot for $50 (see photos). It’s sold for jump starting cars, which really works – I had to use it to start my lawn tractor once. The battery pack has output ports for 12v DC at 200A (400A peak and voltage measures 13.1v fully charged) and a USB port for 5v DC at 2A. It also has an LED flashlight and a built-in charger that accepts 5v DC via mini USB, or 13v DC via a very small barrel connector for use with the supplied auto accessory plug charging cable. The battery is in a hard plastic case, which protects the lipo cells, it’s about 3"x5"x1" and weighs 10.5oz.
I made a cable for the battery from an inline automotive blade fuse holder I got from an auto parts store by adding a ground wire, an EC5 connector to one end that fits the high current output from the battery pack, and PowerPole connectors on the other end to fit my radios (see photo).
I’ve seen similar lipo battery packs for starting cars that have larger amp-hr capacities.
I fly electric fixed-wing and multi-rotor “drones” and handle a lot of lipo batteries. Be careful when using lipo battery packs, especially those that don’t have a hard plastic shell. Lipo batteries can and do “explode,” catch fire, and give off toxic fumes when punctured (exposing the internal chemicals to air), when not charged properly, or overcharged. I have witnessed these things firsthand and so have others on this reflector - Google “lipo fires” to see similar situations. When not in use, I store my lipos in fire-resistant bags specifically designed for lipos, or steel ammunition boxes that I have vented with a small hole for longer-term storage.
If you are going to build your own lipo battery pack, I suggest that you use batteries designed and sold for use in RC cars, which typically have a hard plastic shell to protect the batteries. You should also only use a charger specifically designed for charging lipo batteries. Most that I’ve used automatically stop charging at the proper point. These are sold by the same folks that sell the batteries. Put a fuse in the circuit – lipos store a lot of energy and can discharge at high rates.
The nice thing about the Minimax and similar devices is they address most, if not all the issues I mention above. These light-weight, high-capacity battery packs seem like a near ideal solution for portable operations, but be careful with them.