Have you read this review? Maha Powerex MH-C9000 review
In these kind of batteries the ‘charger’ is just USB voltage in parallel directly into the battery. All charge/discharge functions are handled by the BMS control inside the battery. You should just be able to leave it in the Maha on discharge until it cuts out.
A quote from the review above:
[The discharge was supposed to terminate at 0.9 volt, but terminates somewhere between 1.0 and 1.1 volt].
I use this to do my battery discharge testing: ZH-YU ZB106+ v1.3
# 4 Wire Battery Resistance Capacity Test Holder
I’ve had to make some specialized holders to do thinks like camera batteries and those heated glove batteries.
Works considerably better than the charger/dischargers.
There are a lot of different capacity testers of this type, some with more power, some simpler with built-in battery holders, etc.