just use the charging adapters like TW, Heaven-Gifts (China)and others sell for charging eGo
batteries on 510 chargers. it doesn't look perfect but works.
as i didn't have a charging adapter, i used a 510>901 + 901>510 adapter, it works, but sometimes they get loose and you may end with a 901 adapter inside the tube of the eGo Big atomizer....solution: pliers *örks*