The techniques described herein relate to a trailer tester. The trailer tester may include a tester plug configured to couple to a complementary trailer plug, a battery receiver configured to removably couple to, i.e., receive, a rechargeable battery pack, and a main body. The main body may include a plurality of switches. Each switch may include a positive terminal configured to be connected through the battery receiver to a positive voltage terminal of the rechargeable battery pack, a negative terminal configured to connect through the battery receiver to a negative voltage terminal of the rechargeable battery pack, and an output terminal configured to be connected to a signal light of the trailer through the tester plug.