If budget isn't an issue, then you might want to check Muchmore chargers...
This one can charge 4 batts simultaneously.
MM-HYX4 Hybrid X4 DC Quattro Charger ??????X4 DC??????????????-Muchmore Racing. Co., Ltd.
While this can charge two
MM-HYTD Hybrid Touch AC/DC DUO Charger ??????DUO AC/DC???????????????-Muchmore Racing. Co., Ltd.
They have a few more. Check the site.