Make sure both packs have an identical voltage. Then you can probably get away with parallel charging. After a few parallel charges you will need to make sure that the individual packs are still balanced at the same voltage. If not they will have to be individually charged again. If they are still balanced then keep going in parallel, though individual cells in your pack may get out of balance with the others. Eventually this will destroy cells as some will be charging fully and other will not so lots of strain will be put on the cells that are not fully charging.
Parallel charging is bulk charging which is ok in the short term, but in The long haul you need to balance out your batteries for maximum life span.
And to answer your question...... It may work but will be charged at a lower amp rating due to the charger only be rated to a certain wattage. If in doubt buy a cheap volt meter and put the prongs on + and - ..
