You might try cycling the battery. Unplug it, running from the battery until it drops to about 5 to 10% or until it automatically powers down. Plug it back in to see if it passes that 49% mark and continues to 100%. Do not unplug it until you're sure it won't go any higher.
You also might check to see if Dell has any factory software on there that may be interfering with proper reporting of the battery charge level. If there is, check its configuration.