Biggest batteries I've found to fit in the stock XRT battery tray are these HRB 9500mah 4s 120c packs. The Lectron pro 5200's the hobby sold me are way too small. These
RC Overdose E-REVO 1/16 Parallel battery connector for #2925 (1200 MAH NIMH) batteries - YouTube
Deformed my brand new 2s Lipo Batterys in my E-Revo : r/rccars
Traxxas E-Revo | RC Monster Truck 4x4
E-Revo® VXL: 1/16-Scale 4WD Brushless Monster Truck with TQi™ Traxxas Link™ Enabled 2.4GHz Radio System & Traxxas Stability Management (TSM)® | Traxxas