There is a battery analyzer which can be used to check the condition of battery and health.
It checks the resistance inside batteries.
As you are using the batteries, the resistances of batteries are going up.
If the resistance becomes double of initial value, you should chance the battery. Its capacity will be about 50~60% of initial.
If the resistance becomes 50% higher, it is a kind of warning stage, it capacity will be 70~80%
If you are running a big rental shop, you should consider to use this battery analyzer.
In one second, you can check the health of battery.
============== Initial Resistance ===================
290Wh => 45mΩ
195Wh and 160Wh => 52mΩ
98Wh => 73mΩ