How fast may I trickle charge a full LSD NiMH battery?
How can you tell if the cell has gas recombination capability?

I don't know of any way to tell without asking the manufacturer. If you know of a way, please tell me: I'm curious. That's not something I've looked into. Behaviour at end of charge may well provide some clues.

Anyway, as for traditional NiMH batteries:


The advice from most major NiMH suppliers is that traditional NiMH batteries over about 1800&ndash;2000 mAh should not be trickle charged at all. A few suppliers say you may trickle charge at low mA for a time after charging&mdash;but only for hours, not days.
A few suppliers tell you to trickle charge at C/10. Run away fast from their products.


As for LSD NiMH batteries:


LSD cells are tricky. They have lower capacity per size, but this does not prove they're safe to trickle charge. I'd guess that, at rates well below C/10, Eneloop Lite cells are OK to trickle charge, Eneloop standard may be OK, and that Eneloop XX are not OK to trickle charge. For cells which are safe to trickle charge, C/40 sounds like it's probably an OK figure.