Maybe I'm playing with fire but I've been running two PWs with 20v knockoff DeWalt batteries for months with no low voltage device and have had no issues. Regular DeWalt batteries work too but I bought $25 knockoffs just in case. My girls run them down until the cars stop, I recharge them and they work fine in an hour or so.

By the way, I use this connector: SafeAMP Wire Harness Connector for Fisher-Price Power Wheels 12-Volt SLA Battery https://www.amazon.com/dp/B01INNQ2RK/ref=cm_sw_r_apan_glt_fabc_72WJG06WAS4EMYBF734P?_encoding=UTF8&psc=1