As Jon says, it is always good to have a look at the spec.
Taking the PowerSonic PS1290 spec as an example
http://powersonic.com/images/powerso...10-PS-1290.pdf

At the 5-hour discharge current of 1.44A, the specified capacity for this PS1290 9Ah SLA battery is 7.2Ah.
Richard measured 180 min = 3 hours @ 1.4 Amps = 4.2Ah.
4.2Ah of remaining capacity out of the specified 7.2 Ah means that this battery has deteriorated to 4.2/7.2 = 58% of the original capacity.
If this is a used battery, with a number of deep-discharge cycles, this deterioration is quite normal.
If this a new SLA Lead Acid battery, this is a very poor specimen.

Any rechargeable battery is a consumable.
The capacity decreases with each and every discharge-charge cycle.
The use case has a big influence on the rate of deterioration, e.g: shallow vs. deep discharge.
Looking further down the spec sheet of the Lead Acid battery, in the "life Characteristics in cyclic use" graph, you can see that this battery has a life expectancy of only about 200 deep-discharge cycles (100% discharge) and about 1100 cycles of shallow (30%) discharge.
This is why I run my batteries in parallel.

Similar calculations can be made for the LiFePO4s. I have no specification for this chemistry.
Assuming that the LiFePO4 9Ah battery derates similarly to 7.2Ah at the 5-hour current draw, Richard's measurement would indicate:
280 minutes = 4.66 hours @ 1.4 Amps = 6.53Ah or 6.53/7.2 = 91% of capacity.
Not too bad.

As said, I have all 3 of my fused SLA batteries switched in parallel. I am very comfortable with that (and no, one battery does not charge the other !)
As far as I know, the LiFePO4 packaged batteries have build-in discharge and charge protection circuits. With those, I would need to understand the spec in much detail before I would be comfortable switching them in parallel.
3U