Connector to charge bluetti from other lithium battery sources

I know expansion batteries are your bread and butter but I would suggest designing a product to allow bluetti owners to charge their power stations from existing lithium battery’s they many own. You have a product for lead acid. There are a couple people working on setups right now that they plan on selling to do just that. If you were really smart you would make it universal so anyone with any brand of power station could use it to charge their power stations.