I have a similar XT90 series adapter from hobby king. I think the one I have uses beefy wires, seems like 10ga to me, but I'm no expert. It seems to be the same kind of teflon-coated cable they sell in bulk as 10ga. Either way, it's heavy, very flexible, feels very high quality to me. I wouldn't be surprised if the Ebay one is the same thing, but I don't know. I wonder if some people don't realize how big XT90 is. Some might be used to XT60, which looks identical, just smaller. If you know how big XT90's are, the ebay pic wires look big to me. The xt90 connectors will only take up to a certain width wire anyway, I believe that's the 10ga.
I run two multistars in series for my current little ebike, which only maxes out around 700W by my calculations, but I've never felt the wires be even perceptibly warm, though the lamp cord style wire on the motor side has been felt to be barely warm before. This'll be a more important factor on my next build though.
I need to be able to remove my batteries to charge them. Maybe it's my ignorance, but bullet connectors scare me, and Multistars already come with XT90 connectors. (BTW, the wires on my battery are, IIRC, the same thickness as the wires in my Serial adapter.) I don't have any experience w/bullet connectors, but I've seen them used in videos. Bullet connectors leaves a wire lead exposed. XT90 is less exposed. I really like having the adapters. It gives me peace of mind. With XT90 connectors, I don't have to worry as much about plugging something in wrong. Now when we start to get into using two adapters to put 3 batteries in series, which nobody answered yet, that is a different story. The answer is, Yes, I think you can take the output of 2 batteries on one adapter, feed it into another adapter plus another battery, and then plug that into your motor.
The way I see it, not being very experienced and not wanting to make a mistake, the best way to do things with something approaching a harness with the XT90 system, is to tape up where the non-battery connectors join (motor and to the other adapter), which basically become your harness, once it's done right, so they won't get accidentally unplugged. That way, only the batteries will disconnect, which can then be charged off-bike. When you put them back, if there's an open XT90 connection, a battery goes on there. Easy. I would also come up with a labeling scheme, and possibly use different colors of tape, so I know what each connector actually is. At some point, I even considered a 3S2P setup, where that would've been extremely important.
Hobbyking (not that I'm endorsing them) also sells much smaller, basically solid adapters, with basically no wires in-between. Both serial and parallel, I think. Which are similar looking, so again differentiate them somehow if you get both; or get the long wire adapter for one type of adapter [S or P], and the solid no-wires adapter for the other. After getting the 'wires' adapter like you linked to, I realized the Multistars I have already have a decent amount of wire coming from them, so I found I didn't need the extra length the wired adapters gave, though I thought I might when I ordered it all online.
I'm interested in ebike.ca's Cycle Satiator, as it seems to be an on-bike charging system (in which case you could tape shut only the motor-to-harness XT90's), but I haven't figured out how lipo cells balance using that thing, and discussion I've seen has been devoid of that topic. I can't figure out how the Satiator is anything but a precise bulk charger, even after reading their product page and Justin's OP about it on this forum, but I haven't put a huge amount of study into it. The biggest pain in my system above would be removing each battery to charge it. Which isn't a huge deal if you're not a commuter. But those XT90 adapters can be a b*tch to pull apart (even with some silicone grease on the plastic). I assume when using the Satiator that you have to put separate external balancers on each battery, but I really don't know, and wouldn't mind if someone told me briefly, even though I don't want to push the thread much off-point.
I remember what it's like to be a noob, because I still consider myself one a year later, and his question is a very good one. When most of the senior people started here, the lipo packs were smaller, and usually didn't come with XT syle connectors. I imagine most were bullet or some smaller type of connector, and they ended up making a lot of their own stuff, and changing smaller batteries around in different configurations, which bullet connectors are good for. The idea of accidentally shorting a pack freaks me out, and if that means using adapters like the OP linked to, so be it, despite the soft shaming here (though not ill-intended), not restricted to the talk of silver solder and welders and such, which is silly talk for most newbs. Yeah, you could solder up your own harness, but if you can buy two adapters for ten bucks which does the same thing and is safer out of the box, yeah, that's a valid option. At that point, the only question is whether everything's hooked up right, and the current handling, which would be the same question if you made your own.
