Anyone considering an Optima spiral cell battery
should make a comparison with other AGM batteries.
Because of the spiral cell arrangement, the Optima is larger for the same capacity. The Optima is also more expensive than other AGM batteries of the same capacity.
For example, the Optima D31T (highest capacity yellow top) rated at 75AH sells on-line for $230 ($3.06/AH) while the SunExtender PVX 1040T rated at 105AH sells on-line for $259 ($2.47/AH).
If you take advantage of the $25.00 rebate, the cost per ampere-hour is $2.73; still higher than the SunExtender.
The Optima is physically larger than the SunExtender: its length is 12.8" vs 12.01", it's height is 9.4" vs 8.93. And that is with less than 75% of the capacity.
So if you want to squeeze more capacity in a smaller space at a lower cost per ampere-hour, the other AGM batteries are the answer.
The prices I've mentioned are not necessarily the lowest on the web. A Google search should find the lowest prices.