Battery Charger P4201 (Powerplus POWX4201) is a 12 V smart trickle charger rated up to 60 Ah, featuring an integrated micro‑controller that monitors charge state and automatically switches to maintenance mode when the battery reaches full capacity. Common failure modes include loss of output voltage due to a failed MOSFET or IC, over‑temperature shutdown from a faulty temperature sensor, and micro‑controller lock‑up causing the charger to remain in “standby” with no LED indication. First‑check diagnostics: verify 100–240 V AC input is present and within spec; measure the DC output (should be ~12.8 V at light load) and inspect for any visible arcing or burn marks on the PCB; confirm the internal fuse is intact and that the status LEDs cycle normally during a power‑on test.[oss-gpt-20b]