Why has this daily need to recharge never affected Strax?
These Sontarans look somewhat different: perhaps even though they're a species of clones, some genetic modification went on at some point to remove this weakness?
Or maybe Vastra and Jenny set up something for him in a corner of their house. It's quite understandable that he wouldn't want to talk about it, even to an ally.
For that matter, why didn't it affect the captured Sontaran? He'd been in Mrs. Seacole's British Hotel long enough for her to notice and time the recharge cycle, but he had no access to the ships to actually do the recharge itself.
