use the 85w charger.
"Power adapters for Intel-based Apple notebooks are available in 45W, 60W, and 85W varieties. Although you should always use the proper wattage adapter for your Apple notebook, you can use an adapter of a higher wattage without issue.
For instance If you have a MacBook (13-inch Late 2009) that normally uses a 60W adapter, you can also use an 85W adapter with that computer. You would not use a 45W adapter with that computer; it would not provide enough power for that MacBook. "