But I reckon Training Mode is a better option than running 2S IMO. You get the same benefit of running 2S and yet you don't then need to buy another set of batteries when ready to go 3S
Can you de-tune a Traxxas Slash by using a lower punch setting or turning down your throttle dual rate? If so I'd probably do that and invest in the 3s batteries. My Traxxas is only rated to 2S and for what it is that's fine. If I want to have serious fun, then the Arrma's come out