They're actually E6's , as far as TMCC or even Legacy is concerned for that matter the use of a 9 volt battery is purely optional.
It is not necessary for operation like the battery in a PS2 loco. The 9 volt battery is there primarily to keep the sound from dropping out during direction changes in a conventional environment, or "dead spot" over a turnout during command operation.
I've been using TMCC/Legacy for several years and never needed/added a 9v.
The only drawback( not owning a set myself) would be the obvious 13 years of improvement in sound and operation that has occured since these were released.
Lionel has announced some Legacy E units in their latest catalog, folks could be selling off older units to upgrade.
Heres a link to the Lionel product page for the ACL E6's, at bottom left there is a link to the owners manual as well.
http://www.lionel.com/Products/Finder/ProductDetail.cfm?ProductNumber=6-14524&expandBranch=0&Keywords=ACL&CategoryID=0&RailLineID=&CatalogId=