If a battery has been badly discharged, personally I would try first giving it about a 20 hour rated capacity charge. In other words about a 5 amp charge on a 100 AH battery. I'd check the voltage (disconnected) in 15 minutes after letting it rest for 5, and if it looked to be accepting a charge, continue charging.
If it wasn't, I'd check the cell voltages by probing through the fill holes. If one was low, it probably has a shorted cell. If all were about the same, I'd probably do what Andrew did, which is up the charge rate to try to stir up the electrolyte in case there was sedimentation. But only for a few minutes, keeping an eye on it. Then return to the 20 hour rate.
Not saying that's based on any good authority, just what I'd do.
Long term trickle charged batteries, I personally believe, benefit from an occasional initial 15 minute long 3 hour rate charge (ie ~30 amps on a 100AH batt) to stir up the electrolyte and prevent sediment compaction. Then return to the normal rate.
I lived on a cruising houseboat for a few years with an Heart Interface (brand) inverter and it did just that periodically to extend the life of the deep cycle lead acid cells aboard.