I would also assume that it‘s the battery that is holding you back!
I did some experimentation last week with a non-LiPo solution myself (the „can explode part“ of the LiPo still scares me somewhat).
My solution includes n regular 8-AA-battery holder, a 9V plug, a PF-Extension-Cable and 8 1,2V NiMH AA batteries connected to an sbrick.
The tracked vehicle I am powering with this has 4 RC-Motors and works nicely. The only problem is that the sbrick gets really hot and actually shuts down at 80+ degrees Celsius... ;)
My model is likely a bit lighter than the Buggy, but L-Motors draw less current than RC-Motors also...
At full charge the NiMH batteries provide about 10,85V which is also pretty nice!
I just think that the sbrick might not like that much power running through it for a longer period of time - I am likely going to reduce the load to 2 RC-motors and get a second sbrick...