Troubles with Lead Acid Battery Pack - Getting 1/3 the Wh expected.

[ayeitbeguy]

We have been working on making a battery pack which was expected to have 1800 Wh, however at best we have gotten to 690 Wh.
Some info about our system:
Controller: We are using a Kelly KPM controller with regen on, Max battery current set to 20%.
Stats:
- We usually pull 90-110A
- When pushing on the throttle high enough (90A-110A), it drops 3V (26V->23V)
- We are using 10 Chromebattery 12V 15Ah lead acid batteries
- We have it wired so that it is 24V, photos attached. (5 parallel sets of 2 in series)
Here is everything I tried:
- Checked the connections, made them bolt on so they cannot come loose
- Balanced the batteries
- Trying a newly bought set of batteries
- Tried other setups (see below), which worked completely fine
- Put the positive and negative of the bus bar on opposite sides for more even distribution
Other batteries we used which performed much better.
- Optima YellowTop d34 12v 55Ah, we put 2 of these in series to make 24v, and got around 1300Wh with this.
- EcoWorthy 12v 50ah - We put 2 of these in series to make 24v, and got around 1200Wh
- Note that nothing was changed in the system other than these batteries

If anybody has any suggestions I would very much appreciate it. I am not a professional so perhaps there is some major mistake I am making.
This is what our battery setup looks like:

 

[neptronix]

Capacity ratings on lead acid batteries are typically done at 1/20th of a C ( ~3.25A in your case per the AH of the battery )
You're using the battery at approx 1.25C, so, some discharge efficiency loss is expected. What i don't know is, how much to expect.

What would help is to do capacity tests on each pack at 3.25A ( about 1/20th of a C ) to see if you get 15ah out of them in the first place. If you do, then this might be poor discharge efficiency rearing it's ugly head... or.. your LVC is too high for SLA