Battery power in my LGB 2119d mogul

[emdmike]

I am in the process of installing battery RC into my old 2119d mogul.  RC gear is Locolinc with soundlinc card.  That part was easy.  I am planning to use two 7.2vt Nimh 5000mah batteries in series to get 14.4 volts to the reciever.  BUT, I dont want to have to remove them to charge them.  My smart charger for my RC car wont charge batteries more than 8 cells, this would be 12 cells total(6 in each pack).  Can I use my old charger on trickle mode(overnight) to charge the pair as one battery?  Thats how it would seem electricaly.  I can set it up thru a DPDT toggle with center off, one way to turn on the locomotive, other way to connect battery to charging port.  I was going to try charging them outside of the tender first to see if it works.  Buying custom battery or going to another set up like Li ion ect isnt in the budget.  I get plenty of run time on one 7.2 pack in my Stainz, like over 6 hours, or 5 hours on one back in an Aristo C16, although it was very slow running.  If I can make this set up work, I plan on a similar set up in the C16 but without sound.  I do not use the smoke, so I disconnect it when converting to battery power.   So will my twin pack in series charge like one battery if I do it with a trickle charger??   Thanks  Mike