Battery chargers should be installed as close to the batteries as possible. Why? Because of the wire size. For example, a 30-amp charger mounted within 5' (wire distance) of the batteries can be connected to them with #10 AWG wire, but if battery and charger are 15' apart, you need #4 AWG wire. Not only is 10-gauge wire much easier to handle, but 10' of 10-gauge wire and four crimp terminals cost less than $8, while 30' of 4-gauge wire and four crimp lugs will set you back more than $80. Plus, you will need the tool to install those lugs; they are too big for a standard crimping tool. Soldering, by the way, is not an allowable alternative.