I pulled these parameters off of RCGroups

Trickle charging works the same way for Nicads & NiMH. The basic idea is (if I remember correctly) is:

Slow Charge: 1/10 c
Trickle Charge: 1/100 c

Assuming you mean a set it and forget it charge current for trickle charging.

http://www.rcgroups.com/forums/showthread.php?t=47994

The Capacity of a battery determines what the Trickle Charge Rate should be.

For a 2500mah battery, a Trickle Charge Rate would be 25ma Constant. Most Wall Chargers have been 50mah, and that was based upon the fact that the Tx and Rx batteries that came with the radio were usually 500-600mah. I know pilots who keep their Tx and Rx batteries on charge all year round using a device called Little Trickle, from Ace, I believe. This is, of course, for NiCad and NiMh batteries.

Even at 50ma, with a Wall Charger, it would not hurt a 2500mah NiMh to leave it on for a few days. Check the output of your Wall Charger to determine what it's output rate is.