I am stuck between the Traxxas 2878's and SPC 6500 11.1 batteries. I plan to use them In my Stock Spartan (gen2). How do the Traxxas 8400's hold up? What advantages besides the bigger mah should I be getting? I know the Traxxas 8400's will be heavier but would they fit in a 1/10 Summit/ E-Revo? Feel free to comment or suggest! I notice that the Traxxas 8400's are about $130 each vs. SPC 6500 @ $65 each, so besides the bigger mah what am I getting. I personally think the 8400's are a bit toooo expensive. I need something that will hold up!