Charlton's run of form is legitimately awful. They've lost at home to Gillingham, Burton and Blackpool since the beginning of February. They've picked up 15 points from 14 games since the turn of the year, which is relegation form over a couple of months. They also seem to have a real discipline problem - a glance at their results on Google (which shows the result and any red cards shown to either side) shows they've had five red cards in that run (to four different players - Darren Pratley getting sent off against Hull and then again against Blackpool).
On the flip side, all of their positive results recently have come on the road. Their only loss away from home since going to Hull on 2 January was a 2-1 at London Road, in a game they were winning until over an hour had passed. They scraped past Wigan on Tuesday, who we know are probably a better side than their league position suggests, and have beaten MK and Rochdale to nil in recent weeks - neither feats we managed.
They seem to be a side that can be got at, and I think we're something of a bogey club for them. But judging on those away results, I imagine they'll try to sit in and nick a goal when they can. We've struggled to break teams down recently, so we could be in for a bit of a long, frustrating, attritional afternoon.