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Macbook Pro Charger: 85W/60W/45W - Difference?

Looking at getting a spare charger for my 13" Macbook so I can keep it in my bag for Uni and just leave my other at home.

Straight from Apple's Website:
Apple 85W MagSafe Power Adapter (for 15- and 17-inch MacBook Pro)
Apple 60W MagSafe Power Adapter (for MacBook and 13-inch MacBook Pro)
Apple 45W MagSafe Power Adapter for MacBook Air

So with a 13" Macbook, a 60W charger seems like the one. I then read a comment by someone:
45W - MacBook Airs 11 & 13
60W - 13" MacBook Pro (can also use for airs)
85W - 15" (&17") MacBook Pro (can also use for 13" & Airs)

NB. you can use a higher W than was supplied but do not use a lower W. The 2012 MacBook Airs & Retina MBP's use Mac safe 2

So if that's true and you can use the 85W on all of them, then why bother making a 45W charger too?

To me, I'd see why you can't plug a 85W charger in a smaller battery because it may overpower it, and a 45W charger will take a day and a half to charge a bigger battery in a 17" macbook from a smaller air.

So is what he said inaccurate? If not, why do they bother making 3 different chargers if the 85W works on all? Just doesn't make sense to me?
Reply 1
Avatar for Dez
Dez
20
The 85W charger is about double the size and weight of the 45W one, and hence is about as portable as a breeze block. That's the main reason there are separate types. Also until recently I think they were priced differently, with the highest power chargers costing the most.
Reply 2
Avatar for Camoxide
Camoxide
14
85W is bigger, heavier and costs more to make. Would like silly with the tiny Macbook Air.
85W wont over power the battery. It'll only draw as much as it needs.

The 45W can't power the 17 inch pro.
Reply 3
Avatar for mfaxford
mfaxford
1
As has been said above the laptop will try to pull the power it needs. The PSU ratings are for the power it can supply. If its a small laptop (45W) with a big psu (85W) then there wont be a problem. If it's a big laptop (85W) with a small psu (45W) you'll have problems, at best it wont work very well, at worst it could damage the laptop and/or psu.

The smaller psu is likely to be cheaper and smaller in size because the parts inside don't need to handle as much power. You might also find the PSU is more efficient (less energy wasted as heat)

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