t max duel battery system

hi all for crimbo wife got me a
t max duel battery charging system.
as one off the other members has said to me he has put fuses both end of the main cable.
which i will do. but in the instructions it says nothing about fuses.
if i do want to link the batteries would a 100amp fuse blow pretty quickly
http://www.ebay.co.uk/itm/170588370331?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT
mine is the same but its got a 270 amp relay
j

For charging, a 20 Amp fuse would be enough. 100Amp could cause a fire should a short occur. The fuses protect the wire between the batteries.