Add a lithium house battery for your electronics. You could also move over your stereo, lights, pumps, etc. Then all you'd need for your big motor is a lead acid cranking battery, and you could probably drop down a group size to save some weight.
There are DC to DC lithium chargers that allow you to charge off a motor alternator. I haven't looked into them yet so I don't know how well they work or what the cost would be.
I know a few walleye and bass pros sponsored by dakota lithium. They have nothing but good things to say about them. I also know a few guys that have run 3-5 dakota batteries in their boats only to have issues and receive horrible warranty support.
Personally, I'm just going with cheap lithiums off amazon. Li Time, Wieze, etc are all highly rated.