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RC lithium polymer batteries should be fused as they can sink up to 50 A.
When designing a box, circuit layout, or other assembly, keep in mind that wires and electrical components do take up space. Leave clearance in the design stage; this problem should be solved before fabrication/assembly.
If possible, put hot-swappable components such as batteries or modular PCBs in locations where they are easily accessible.
Use standoffs to make sure the circuit board has good isolation from what’s beneath it. This is especially important if the board is mounted on a metal plate.
When using shielded cable, ensure the shield is properly terminated and grounded.
If it’s conceivably possible for a component to be installed backwards, there should be idiot proof documentation of which way it goes, that documentation should be less than 2 inches from the install point.