E240 Mercedes estate X Reg battery flat no mains available

I am keeping an E240 off road for 12 months in a yard without access to mains electricity. The battery is flat (doors won't open by remote no signs of life). If I take the battery out to charge it is it going to mess up the electrics? I'm not that technically minded so if it's a risk may have to call someone out? Advice please. Thanks


Mercedes Benz E Class (1995-02), E240 5 Dr Estate 2.6 V6 Elegance Auto
X Reg 140,000 miles