[G6Tanuki]

Tour original post says the battery-packs are "quite old" - just how old?

NiCd cells are usually rated for a specific number of charge/discharge cycles [the two-way-radio ones I worked with in the 80s and 80s this was typically 500, equating to less-than-two-years of service]. They also degrade with age even if they're not being subjected to regular charge/discharge - indeed, regular use seemed to keep them healthier than sitting on a shelf unused for a couple of years. NiCd cells have issues with 'self-discharge' and I had a rather draconian policy of discarding any packs that had sat unused for more than a year [if only to avoid annoyed clients whose battery-packs that were supposed to work for a day of 9:1 receive;transmit duty-cycle shut-down prematurely].

NiCd technology is now long-obsolete anyway; perhaps it's time you should be upgrading to Lithium-Ion stuff [lots more Milliamp-hours-per-gram-weight of battery-packs, much less self-discharge in infrequently-used devices]