Vintage Simmons Drums (UK) Users Group

I have a Simmons TMI that no longer can keep its memory when shut off. It needs a new battery. I tried to change it, but I'm not sure what kind of replacement to get for it. It has this written on it:

"Emmerich 3,6"

So, I assume that it is a 3.6v battery. But, I don't know the amps. It is about the height of three coin size batteries stacked together. 

Does anyone know what I can use as a replacement for this battery? 

Thanks,
Erick