For enhanced power performance, the LP-E4 battery has been redesigned and is named as the LP-E4N. The inside of the battery now uses a larger number of smaller cells and so the battery capacity has increased from 2300mAh to 2450mAh. Because many people will have a collection of LP-E4 batteries from their previous EOS-1 series cameras, they have been made both forwards and backwards compatible, so an LP-E4N can be used in an EOS-1D Mark IV and an LP-E4 can be used in an EOS-1D X.
There is also a new charger to go along with the new LP-E4N and this is the only charger than should be used with the new battery. If an LP-E4N is charged in an LC-E4 charger you will not fully charge the battery; instead it will only reach around 90% charge so your capacity is reduced and it will not meet new safety regulations. However, an LP-E4 can be charged in the new battery charger with no problems.