Unless the charger rides on the car, it shouldn't count against your $500 limit, but unless you can come up with an exceedingly clever way to characterize a lightweight battery as safety equipment, it probably does count against the $500 limit:
"4.5: Sponsorships: Conned some hardworking corp into giving you parts or cash? Nice work, but it still counts toward the $500 total."
For budget purposes, it would make more sense if your buddy could just buy the lightweight battery at a discount, but beware of the rule against rationalizations:
"4.1.1: Lame-Ass Rationalizations: Cars that "should be" worth $500 don't count; cars that "were worth $500" before you spent another $2000 to fix them don't count; cars you've owned for 20 years and spent more than $500 on during that time don't count; "it would have been worth $500 if it didn't already have a cage" doesn't count. Five hundred dollars means five hundred frickin' dollars."
Cheers.
Pat Mulry, TARP Racing #67
Mandatory disclaimer: all opinions expressed are mine alone & not those of 24HOL, its mgmt, sponsors, etc.