Josh, I think it'll be much easier to recommend a system if you told us your budget, usage and size requirements. Otherwise people will just start suggesting what they have which may not help you at all.
Battery canisters shrunk when NIMH cells came out.
Steve you are probably thinking about big lead acid packs that manufacturers use to offer before Nimh and lithium battery packs came out. Some still do come with lead acid packs, stay clear of those, they are just to heavy.
Ron and Tman, are you suggesting Steve is ...errr... old skool?
:)
NiMH batteries have been out for a long time. I've been using them for the last 10-12 years at least. Before that was NiCd and lead acid, which are toxic and NiCd is now (or going to be) even banned in the EU.
Sure putting the batteries on the bottom of the housing for lights is nice for macro except the pods don't allow the housing to get down low... which sometimes is more important than the diver getting down low.
Furthermore, to get brighter lighting for WA, the battery pack has to be bigger. If one looks at the Gates setup for the Squid 250, the battery packs are also on the housing. This helps with inertia and handling but balance will have to be adjusted based on lens setup and also overall buoyancy. No free lunches.