Defender Paddy McCarthy scored a last-minute equaliser to earn Charlton a point against his former club.
McCarthy hooked the ball through a crowded penalty area and into the far corner to deny Leicester back-to-back wins for the first time this season.
Stephen Clemence gave Ian Holloway's men the lead when he headed in Richard Stearman's cross after 78 minutes.
After a dour first half the hosts began to dominate but Charlton threatened on the break and struck at the death.
Leicester manager Ian Holloway:
"This was the most patched-up team I have ever fielded and we got a draw but it should have been a victory.
"The players gave me everything after the break and I can't ask for any more than that.
"But we are devastated that we were not in the dressing room celebrating victory after the final whistle."
Charlton boss Alan Pardew:
"We showed character, dug in and got something from the game, which we deserved.
"It is a point in difficult circumstances in what was a stop-start game in difficult conditions.
"To concede the goal when we looked really comfortable, it looked like being one of those horrible days that you get in the Championship."
Leicester: Fulop, Stearman, Kisnorbo, McAuley, Mattock (Sheehan 15), N'Gotty, Kenton, Clemence, Hume, Fryatt, John (Hayes 22), Sheehan (Wesolowski 76).
Subs Not Used: Henderson, Ashley Chambers.
Goals: Clemence 78.
Charlton: Weaver, Bougherra, McCarthy, Fortune (Moutaouakil 65), Powell, Jerome Thomas, Semedo (Sam 80), Zhi, Holland, Varney, Iwelumo.
Subs Not Used: Randolph, Racon, McLeod.
Goals: McCarthy 90.
Ref: Scott Mathieson (Cheshire).