G300! Great choice, I love mine.
Are you sure(?) it should be a cylinder thing with two metal leads in a bag with the connectors.
Short answer: kinda yes? But no. Once the battery is connected, it’s fine. The issue is plugging it in- you want to have the pre-charge resistor for this.
Long answer: Without a precharge resistor, when you plug in the battery there’s going to be a big spark. The high-temperature plasma from the arc damages your connector terminals(and can be quite loud). You could maybe accept this damage? I wouldn’t recommend it.
The reason you need the antispark is the G300 (like most vescs) have big capacitors across the power input to smooth the power flowing from the battery into the controller. A side effect of this is when you first apply power, a ton of current rushes into the capacitors, causing the spark.
Having a resistor in series with the battery significantly slows the rate they charge, preventing the arc.
Once the battery is plugged in, you no longer want to have this resistor in series because it’ll restrict power flowing into the G300 (and also likely overheat).
The reasons illustrated above is why this solution is so convenient. Take a look at this AS150 connector (what I have on Ankle Wreacher)
It is a two tiered contact. When plugging it in, initially only the tip makes contact initially. The tip is connected in series with a resistor inside that prevents a spark. Then, as you continue to push the pin all of the way in, the socket will also contact with the side of the male connector, allowing it to bypass this resistor.
If you don’t want to use an anti-spark connector, and/or you can find that pre-charge resistor that they shipped you, this is an option;
- Plug in the negative of the battery to the g300
- Holding the pre-charge resistor with a pair of pliers (because it could get hot, bridge the battery + to the G300 +.
- Hold for 5~10 seconds to make sure the capacitors are fully charged.
- Quickly drop the resistor and connect the battery+ to the G300+. The faster you do this the lower the chance there will be a spark (the capacitors slowly discharge when no voltage is applied) (Metal-to-metal contact is fine, you can take your time with the bolt/screw)
A bit Janky, but I do this whenever I need to unplug/replug Ankle Wreacher and haven’t had an issue since. (Even though I have AS150 connectors, I destroy the resistor inside a AS150 because rated for the current surge that 4x G300s pull when plugged in simultaneously at 16s)
I posted about it in my thread, you can see an example of the contact damage that can happen when there’s no anti-spark:
Also, don’t forget to use the rubber insulating rings below your terminals 
The housing of the G300 is connected to ground, so you don’t want stuff shorting to it.