Before using rechargeable cells I check the 'dead' voltage of the primary caell. Some clocks, for instance, will run down to about 0.90V; others peg out at 1.3V.
Thanks for the warning. The NiMH I got from Aldidl are so dark and have such small printing that the "Ready to use" is the only easy way to distinguish them from equally dark primaries.
BTW, 'Made down to a pound(land)': AAs at 800mAh and AAAs at 300mAh - talk about taking the piss!