[rhylsadar]

hi
i would not buy two chargers but rather one that can handle the needed number of cells. in your case 18 or above.
you should treat the two packs as if it was only one pack. charging them connected serial will give be the best way that the packs deliver the same capacity. if you haven't charged them togehter so far they should be formed up first. that is the 1/10 C procedure explained above.
that will make sure that the packs are as equal as possible. then you can charge them as if it was one big 18cell pack.
the delta peak cut off rate is lower for nimh cells than for nicd packs. that is why you can overcharge nimh cells using a nicd charger.
so be aware to buy a nimh charger or better one where you can set the cut off rate by yourself. (around 20mv per cell for nicd and around 10-15mv per cell for nimh are the numbers that are known te me).
as for chargers i could recommend one that can handle up to 25-30cells and charge with up to 5A. don't know what is commonly used in the us. (in europe that would be something like the intelli V3, gm vis commander or schulze d330)
the powersupply unit should at least deliver 10A.
bye
rhylsadar