Two of my favourite bike lights got spoilt recently with battery leaks (stocked with that white salt-like deposit inside).
Any tips on how to clean that recover that white residue and recover the lights? Or are they gone for good?
Acid or alkaline?
There are easy ways to clean them and hopefully recovery your lights in working order.
Firstly you'll want to get rid of anything that easily flaked off, for that, use an old soft toothbrush
If its acid you want to use baking soda on a cotton bud
Alkaline you want to use lemon juice or vinegar, again on a cotton bud.
All you can do is try to clean them as best as you can, electronic circuits are safe to clean with a cotton bud, as long as the circuit is dry when powered up. Corroded contacts probably won't be recovered to their former glory so easily, use a cotton bud or baby wipe to remove as much of the battery deposit as you can (use gloves the alkali used can react with oils and fats in your skin).
The batteries are Duracell AAs, so I assume they're alkali?
If so, I should first try to dry remove the deposits, then clean the rest with cotton buds and vinegar, right?
Yeah, get as much of the dry deposits off, without applying loads of pressure and then a little vinegar on a cotton bud and give it a good clean. Then sit for an hour to dry off.
Should work, make sure its fully dry, then put some new batteries in and it "should" work again.