http://www.batterysupports.com/44v-48v-504v-12s-30a-12x-36v-lithium-ion-lipolymer-battery-bms-p-268.html
33€ + 7€
https://www.banggood.com/es/44V-48V-50_4V-12S-60A-Lithium-ion-Li-ion-LiPo-Li-Polymer-Battery-BMS-Protection-PCB-Board-p-1116752.html 29€
They look exactly the same constructed, but there is a remarkable difference in price.