Yes, there is.
On my 2007 ES 350, it's a CR1632 button cell. I had a little trouble finding one locally when mine died. Even the Lexus dealer didn't have it! But I finally did find one at a larger Radio Shack store.
Just remove the metal key from the fob, insert it into the slot exposed near where the key went, and pop the fob open. Insert the battery, and you should be all set.
This link will show you how: http://www.youtube.com/watch?v=Za7pCdUde3U
CR1616
CR1616
Open the key fob, remove the battery and look and see what size it is.
Open it up and check and see.
the key fob battery is the battey in a key fob torch
Panasonic CR 1616
To replace the battery on a Mercedes ml 350 key fob it is probably best to ask the supplier where it is purchased or there may be some instructions online.
Use a dime to open the key fob battery door on the key fob. New batteries are typically available at Radio Shack. Salesperson at same usually know how to open it.
3 button fob 2003 onwards cr1616
Lithium CR1632 (2008). I just replaced mine and got it from the dealer.
A small battery that fits in a key fob or remote.