This is my understanding of how you are thinking about connecting your XP-3 to jump start your bike.
[Bike battery]--[Optimate pig tail]--[Optimate pig tail]--[XP-3 pig tail]--(XP-3 jump start battery)
_________________
(ring terminal / SAE)_________(SAE / Clamps)________(Clamps / EC5)
In your previous post you said "I’m not that confident that the Optimate charging cable would handle the sort of current required for starting so my plan B would be to connect direct to the battery."
I would agree with your concerns and your plan B.
The sticker on my Optimate-3 lists the output current as 0.8 amps. The pigtails that come with it are both 18 AWG with SAE connectors (one with clamps and one with ring terminals). I'm not sure what the SAE connectors are rated at but I think they are generally used on circuits that are 15 amps or less.
You are talking about a much higher current to jump start the bike with the XP-3.
What I am suggesting is:
Keep your pigtail (ring terminal/SAE) on the battery for your Optimate and other accessories.
Add a second pigtail (ring terminal/EC5 connector) so there is just one pigtail between your bike battery and XP-3.
You can order one from Antigravity that has some protection built into the harness or see some of the suggestions above for pigtails on ebay or Amazon.
I have two ring terminals on each of my battery posts.
- One to a fuse box that feeds other circuits.
- One to a Clampless Harness for my jump start battery.
The ring terminal on the Clampless Harness had a much larger diameter so I put it on first.