As I said in another post,  I replaced my 4 Victron 165AH AGM batteries with 6 Firefly Carbon Foam batteries.   I looked at lithium batteries and decided that the potential extra performance wasn't worth all the changes I'd have to make.   By doing what I did,  I stayed with standard form factors, standard equipment, standard metering, etc..

To recap,   the Victron 165's were only 3 years old and would drop down to 11.x volts at 75% SOC.  While they are rated at 165ah,  most of that seemed inaccessible given the above.   My frig and freezer would cut out at 11.x volts and the inverter has cut-off voltage around there.   Not pleased with their performance.   I even had a solar panel on the winter cover to trickle charge them over the winter, but they still didn't hang in there.   My prior boat's 8D lifeline batteries would give me 5 years or so.

The FIREFLY G31s at 116AH, so with 6 I ended up with almost 700AH in the bank.    In testing with only 4 batteries,  I found I could draw down to 50% and still have 12.75V showing.    Far better than the Victron batteries.    I then decided to go ahead and add the last 2. 

While the Victrons are larger in dimension, you cannot get more than 4 of the Firefly in the original 575 battery box.    I had to add 2 more in the compartment under the settee forward of the battery box. 

So far,  I am happy with this installation.   Just some starboard bracing screwed into the stringer and strapping as per the original install.   

See pictures.

Rick