I came across this recent youtube comment[1] on why older batteries didn't leak. I don't know if it's correct but sharing it anyway:
>ceptimus 2 weeks ago (edited) >> Old alkaline batteries contained mercury, which made them resistant to leaking. The mercury was there to absorb the hydrogen gas, which builds internal pressure when the battery is used, causing them to leak. Newer alkaline batteries don't have mercury, because it's harmful to the environment when disposed. Unfortunately, the mercury free batteries leak much sooner - many of them long before their 'use by' date, even if you've never used them. Now you've replaced the batteries, you should check the camera more frequently. The modern rechargeable Ni-mh batteries, with a low self-discharge rate, are a good alternative: less likely to leak; but they're only nominally 1.2 Volts per cell instead of 1.5 volts, so some equipment won't work with them.
EDIT... maybe there's more to it than just mercury because some low-effort googling[2] found that law prohibiting it in batteries was 1996 (~25 years ago). That doesn't match the timeline in the video because Alec says his old batteries (that didn't leak) were "use-by-date-2016". So maybe something else was different about the formulation in his Kirkland Signature batteries circa ~2008.
>ceptimus 2 weeks ago (edited) >> Old alkaline batteries contained mercury, which made them resistant to leaking. The mercury was there to absorb the hydrogen gas, which builds internal pressure when the battery is used, causing them to leak. Newer alkaline batteries don't have mercury, because it's harmful to the environment when disposed. Unfortunately, the mercury free batteries leak much sooner - many of them long before their 'use by' date, even if you've never used them. Now you've replaced the batteries, you should check the camera more frequently. The modern rechargeable Ni-mh batteries, with a low self-discharge rate, are a good alternative: less likely to leak; but they're only nominally 1.2 Volts per cell instead of 1.5 volts, so some equipment won't work with them.
EDIT... maybe there's more to it than just mercury because some low-effort googling[2] found that law prohibiting it in batteries was 1996 (~25 years ago). That doesn't match the timeline in the video because Alec says his old batteries (that didn't leak) were "use-by-date-2016". So maybe something else was different about the formulation in his Kirkland Signature batteries circa ~2008.
[1] https://www.youtube.com/watch?v=m5s6xerRqVY&lc=UgztQzUKV5BJQ...
[2] https://www.google.com/search?q=mercury+removed+from+alkalin...