Rechargeable batteries including RAM (rechargeable alkaline manganese) batteries are specially designed to help reduce this risk. REF
If you limit the voltage the the battery can never reach over voltage which is the primary risk cause of constant current failure. So you could charge it with 100mA forever as long as the voltage is shunt limited to 9.0V.
The reason everybody says DO NOT CHARGE more than xx uA is because the voltage can increase beyond the safe limit of 1.525V per cell. So if you have a 9.0V clamp, you are safe to charge any reasonable power in mA you want. ( <100mA <= 1/4W from ESR ) I said SAFE but it may reduce life expectancy on some depending on quality leaks. so 100uA is harmless if voltage limited. But they dont tell the public this so they can sell more batteries.
I had once re-charged Alk. 9V batteries safely with 10mA for long periods. You can recover 10% of the capacity or keep on float at 9V from occasional drain.
To do this use a 9V limiter with series R for ~3mA from 12V or 1k Ohms.
9V limiter can be 3 white 3mm LEDs in series with 33 Ohms ( or 100 Ohms with 5mm LEDs) across battery
simulate this circuit – Schematic created using CircuitLab
But that was 40 yrs ago and I never did long term testing on every battery OEM.
-cheap Alkaline batteries can self discharge when left alone , then leak H2 , break seal then leak strong Potassium Alkaline that dries to white powder and cleaned with Vinegar. Reverse charge might accelerate this leakage on good batteries like Energizer with guaranteed shelf life..
Alkalines are pretty linear 1.10 being dead and 1.535 or so being new/full. and 9V cells use 6S cells in series.
We know Ah capacity are often linked to mass of the battery.
Energizers are 50gm per 9V cell in bulk
Sony 9V cells are 57 gms. (better?)