I am considering adding a 4th battery to my boat just to run the electronics. When I say electronics, this includes today - 2-Helix 10 HD SI units, and a ethernet switch, in the future these could be upgraded to Helix 10 Mega SI G2N units and add a 360 unit on the transom. I am upgrading my onboard charger from a 315 to a 440 since I got a deal on a 440 that was cheaper than a 330, and that gives me an extra charging circuit. my existing current drain on the battery is only about 3.5 amps, upgrading everything and adding the 360 would put my current drain up close to 6 amps. Based on this load, a group 24 battery should do the trick and a group 27 battery would add a bit more cushion and also allow me to jump start the big motor if the main motor battery died for whatever reason.

But I guess my questions are:
1) is the added weight worth the dedicated battery for the electronics?
2) should I be considering a starting battery or a deep cycle battery?
3) what am I missing?