How about 6v or 9v LiFePo4 lithium batteries. Anybody play with any of these yet? Doing some research, may need charge controller even with low watt panels. Steady voltage, high cycle rates. Starting to find some at reasonable prices, compatible with good SLAs. Should last much longer than SLAs. Like lithium flashlight battery, 3.2v per cell, so 6.4, 9.6, 12.8 volt available similar aH ratings to the SLAs we have.