I've got a Tekno With Max8 combo with a XT90. I've got 2 almost Brand new 4s batteries with the deans T plug on them. Is it ok to use an XT90 to Deans Just for backyard Bashing? I don't want to buy anymore Batteries for it cause these are New.

You could, but adapters always add electrical resistance and possible points of failure. Any reason you don't just change the connectors on one side (ESC or battery) so you can connect them directly?

I've just never Soldered any lipos like that before. I guess I'm skeered 😂

If you ever do, just make very sure the cables don't touch. It'll be a hell of a short, otherwise (and it won't be pretty, despite all the sparks.)

So it's best to just snip one from plug and solder it onto new one, Then snip the other one off plug and Solder it?

Yep.

Though the resistance of these plugs aren't that high, so for backyard bashing use it's fine to use adapters.

So the deans plug on my batteries is ok if I run a XT90 to Deans Adapter is that what you're saying?

Just a PITA in the long run (compared to not having to use them), but they won't hurt.

Deans to XT90 you can get adaptors. If your comfortable in soldering make your own. just order on Amazon Sparkless XT90's since you are running 4S lipos.

Like said earlier, if you try to solder a new connector on the battery, do ONE side at a time. You won't like the result if the two battery wires come into contact with each other. Also, make sure the solder job is good, won't help at all with resistance if there is a poor solder joint.