Is the charger gold or black? Gold is old and black is where it's at. The gold charger will have a loud fan noise as the blacking e will not. When it's turned on. Those chargers will not turn on unless they see over 18 volts. You need to check your volts at the battery connector. Black on negative and red on positive. Checking DC voltage. Sorry I don't know how green you are or anyone is for that matter. If below 18 volts you need to truck the charger. You can do that by grabbing another truck (pallet jack, epj, wp). Take the battery connector from the good truck (battery side) and plug it into the bad truck (truck side). This will give the bdi a false service charge reading. Let it sit for a few minutes. Then disconnect and plug connectors back to normal positions. Use all safety equipment required for handling battery's. Then plug in charger and see if the fan turns on now. Or check your volts at the connectors again. See if it goes up from what ever it was at. You really need a dc amp reader to do this properly. Because sometimes the chargers will be putting out the volts but not the amps. If this didn't work. Get the trucks next to each other again and plug both battery packs into each other. While wearing safety gear. This will charge the other battery pack. The battery's will balance out. Let it sit for like 20 minutes. Then plug back to normal and try charging. If it's over 18 volts and still nothing you have a bad charger. There are more options as well. You just need to get creative. Let me know if that helps and if it doesn't I have more things for you to try. Good luck.