UN 3496 only applies to ocean transport. For air transport, the shipper must
abide with SP A199 and enter the words “Not Restricted” on the AWB.
Now, the problem here is that the nickel-metal hydride battery in question is in a defective state. Airlines are sensitive with defective batteries as they are more liable to produce heat. As you know defective lithium batteries are forbidden from air transport. Although not spelled out in the regulations, any defective batteries will more likely face rejection for carriage as the airlines do not wish to take chances. I would recommend to have this defective nickel-metal hydride batteries to be shipped by surface transport. A shipper’s written guarantee that the batteries will not explode or react dangerously cannot be a 100% guarantee.