Thomas Distributing show that they distribute Eneloop NiMH batteries which I wonder about in OP.

I did check with Panasonic and they say they recommend NiMH so I assume I shouldnt be using NiCAD and cant recharge Lithium ones. So how far can I push the milliamps realistically? And, again, is there any way of testing whatever I do end up with please?

I suppose I can just charge them along with the present batteries and leave them next to each other for a few days and see how long they last before they die. But that says nothing about how long any batteries I get are going to LAST?