Combining batteries

Hi all,

I'm new to the site and have been scanning the forums for info on my EV conversion (that I just started planning)

I have a question that I haven't yet found an answer to in searching.

It seems that there is a tradeoff in battery selection between power density and energy density. There has been some discussion about using ultracaps with you batteries but that has been deemed too exspensive an option more most...

My question is, what would happen is you paralled two types of batteries for your system? for example a set of headways with a set of thundersky's?

esentially using the headways the awy people have been talking about using the ultracaps...

would this damage your pack in any way?
seems to me that the headways if placed properly could "dump" charge since thry have a higher rated dischage rate and the thundersky's would provide the needed Ah for max range.

let me know what you think!