For model 4845XL, you will start by removing the 4 screws on the back of the shaver. You will need to push up the trimmer to access 2 of the screws. Once screws are removed, the back cover will lift off and you can then see and access the batteries. The batteries are soldered to the back of the circuit board. For easier replacement, it is sometimes suggested that you use a modified installation technique. This is to break the tabs off of the old batteries rather than unsoldering them from the circuit board. This allows the old batteries to be removed but leaves the tabs attached to the circuit board. You can then solder the tabs from the new batteries to the old existing tabs.
You will find replacement batteries at shaveroutlet.com. See link below
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For model 4845XL, you will start by removing the 4 screws on the back of the shaver. You will need to push up the trimmer to access 2 of the screws. Once screws are removed, the back cover will lift off and you can then see and access the batteries. The batteries are soldered to the back of the circuit board. For easier replacement, it is sometimes suggested that you use a modified installation technique. This is to break the tabs off of the old batteries rather than unsoldering them from the circuit board. This allows the old batteries to be removed but leaves the tabs attached to the circuit board. You can then solder the tabs from the new batteries to the old existing tabs.
You will find replacement batteries at shaveroutlet.com. See link below
http://shaveroutlet.com/shaver-battery-pack-for-most-norelco-more-p-278.html
If you are not able to do this yourself, shaveroutlet.com can do it for you. See link below
http://shaveroutlet.com/professional-battery-replacement-for-most-models-p-374.html