I happen to know a wee bit about Lithium Ion...no you can't mix with other chemistry batteries.
They are still expensive however our boats don't need 400 Volt systems like the Chevy Volt. So, we only need 4 cells in series rather than 96 to 100. We can therefore focus on capacity. You could build a nice house bank using 4 parallel strings of 100Ah cells from Kokam 4P4S giving you 400Ah @ nominal 14.8V. The beauty of such a thing is the ability to dump 200+ amps into a recharge all day long without concern for the battery
cycle life. You would however need a battery
management system to monitor
battery SOC and health
. The cost of the Cells alone would only be a part of the total cost at 16X$200ish.
Weight is only 36kg!!! If you are a racer
, this is the answer to all your needs.
It might be better to go with a higher voltage configuration and then use a DC-DC converter.