Testing individual battery cell with load applied (how many amps should I apply?)

You perhaps was talking about module (7.2V) not cell (6 cells in every module, 28 modules in your Prius).
If you are going to compare your results with someone's else results - you both use the same method, same currents.
It is important how modules behave under the same load in the pack.
Capacity measured at high currents will differ from measurements taken at lower currents.
6A is OK.
My tools are only for professional use and not for individuals.
But you can get an idea of how battery behaves under load from my videos here: www.hybrids.co.nz - YouTube

 

This is an old thread, but the question is still a good one.

The official rated capacity of Prius NiMH modules is 6.5Ah (aka 6,500mAh).
The meaning of this is that applying a 6.5A load will fully discharge the module in 1 hour.

In contrast, NiMH battery manufacturers generally apply a C/10 load current to rate the mAh capacity.
For Prius NiMH modules C/10 is 650mA (aka 0.65A).

As stated by kiwi, higher load currents will reduce the measured mAh capacity. Therefore testing at 6A will never give a result of 6.5Ah. However this does permit completing a test in less then 1 hour. 6A is OK when comparing a group of used modules to each other as long as all are tested at the same discharge rate.

Because I'm a retired Prius owner with time to spare, I do my module testing with a 1A load.

 

I recently obtained a 100 amp battery tester designed for testing standard lead-acid 12V car batteries. Soon I'll have more to say about using this type of battery tester.

When testing a single Prius module (7.2V) the current drain of this variety of battery tester is 60A, not 100A. The load resistor inside the battery tester is a fixed value of 0.12 ohms (aka 120 milliohms). So when the applied voltage is lower, the current flow is also lower.

The battery tester applies load current only while the user operates the spring-loaded "test" switch. The instructions provided with my tester warn against holding down this switch for more than 10 seconds because that would overheat the load resistor inside the tester. When I've used my battery tester I hold down the test switch for <5 seconds. This is long enough to get useful results.

A 60A load current is appropriate for the Prius. This is towards the upper range of the maximum battery discharge rate used by the Prius. Note: In the Prius such large discharge currents occur only for brief periods. Often the largest current spike is when the Prius uses the HV battery and the electric motor-generator to start the internal combustion engine. There is also a large current spike when accelerating rapidly from a dead stop.