Ring alarm basestation gen1 new backup battery

I've been trying to look online to buy a new back up battery for my Ring Alarm Basestation. Because I couldn't find it I've been chatting with support and they advised me to call support. Talked with support by phone and they couldn't provide me with a new battery. They advised me to buy regular lithium batteries at a retailer. When I told them it's a ring battery pack they still told me I should try an (online) retailer. But they don't have it either. Anyone knows how to get a battery? I do not hope the only way to realize that is too buy a new base station. That isn't very customer and environment friendly.