The driver indication that the NiMH battery needs attention is that the fuel consumption will go up ......so if the fuel consumption is within manufacturers' spec, then for practical purposes the battery is OK.
First time buyers of a used hybrid usually worry about the condition of the battery because they dont realise that fuel consumption will provide the answer because battery condition usually deteriorates gradually with the corresponding rise in fuel consumption.
Its not rocket science!
PS: If you are having a transaxle oil change please ensure that special Hybrid (non conductive) oil is used.