Using another Magsafe on MacBook Air

You can do it but because of the massive difference of electricity you can only do it for like 10 minutes at a time. I once forgot my MagSafe charger at home for my 15" MBP and the teacher at school had a 17" MBP and I used his for for short bursts of time and it worked and i still have my laptop

 

I don't know if that is a good idea. You know how hot it get's when you charge it. I would be worried about the heat that would generate.

 

I've used my MBP charger for months on my first Air without issue. Used a MB too, no problem. Thing still works like a champ.

Can't work the other way though. The MBP scoffs at the puny output of the Air's magsafe.

 

Higher wattage adapters have no problem with low wattage batteries. The batteries only 'pull' what they need, the power isn't 'pushed' from the power adapter.

If you try it the other way though, low watt adapter with a high watt battery, the battery will try to pull too many watts and overheat the adapter. Possibly destroying it.

Oh and to answer your question, the watts don't affect the charge time, it's the amperage.

 

it's all good

You can mix and match Apple laptops and magsafe adaptors.
The power supplies are regulated so I don't believe safety is an issue - I think all switched mode power supplies limit their minimum current output too.

I have charged my MBA with MacBook Pro and MacBook power supplies in the office, and charged new MacBook with MBA power supply.

Very few people died.