TA posted about LiFePO4 batteries a while ago.
Using the Tenergy 10AH batteries, I'm impressed. Lighter, longer lasting.
6 hours of ClearNav, 302, 6201 and TT21 brings two 10AH batteries "down" to 13.1V. The old SLA and AGM stuff I'd been using now seems rubbish.
The Lithium Phosphate batteries even use your existing chargers.
Jim