Hi,
any ideas whether there exist one? So far I only found the Opus BT-C900
Not many of those around.
That means there is another?
Only know the C900 and it´s rebadges
Not to divert you from your cause, but I’m not sure it’s worth it. ALL the NiMh 9v are pretty damn poor. Not enough room for reasonable capacity.
I have had vastly better results using 9v LiOn. I’ve got some iPowerUS that are 10 years old and still working OK. Good enough I use them in smoke alarms and DVM instead of alkaline.
Also some EBL that are merely OK. Not nearly as robust. Lose capacity way sooner.
I charge them with a hobby charger (proprietary chargers available), and can do capacity testing on them also.
You could test 9v NiMh that way also.
I have already some 9V NiMhs, that´s the reason 
A charger which can do both would be also nice