Note 5 - Supplemental Balance Sheet Information - Summary of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Goodwill balance	$ 26,753	$ 20,109
Acquisition of SWE		6,534
Effect of foreign currency translation	265	110
Goodwill balance	27,018	26,753
Battery & Energy Products Segment [Member]
Goodwill balance	15,260	8,616
Acquisition of SWE		6,534
Effect of foreign currency translation	265	110
Goodwill balance	15,525	15,260
Communications Systems Segment [Member]
Goodwill balance	11,493	11,493
Acquisition of SWE		0
Effect of foreign currency translation	0	0
Goodwill balance	$ 11,493	$ 11,493

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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