When I start my main motor I get a low voltage warning on my Helix 10 SI.  I hear this may be bad for the device. Is that something that can damage your device over time?  If so what can be done to prevent this?  I am running my finder off the starter battery obviously. Will a two battery 12 V system solve this issue or perhaps a larger deep cycle battery?

What size battery?

is the unit wired directly to the battery? What gauge wire did you use?

Switch on the sonar unit after you start your OB. Your battery is either weak, poor connections or undersize.

Tom

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These new units will drain a starting battery faster than the older units.  With two running on my new rig I found my starting battery too low to start the engine after about 8 hours on the water.  They have power saving features, easy to use and saves battery when not really needing them on.

 

I also bought a  jump starter power unit just in case. Takes up less space than jumper cables, and on my boat it's a lot easier to use than jumping from the trolling motor batteries.

 

The unit is wired directly to the starter battery. The wiring is 14 gage I believe until you get under the dash then it changes to the power lead that came with the unit. I am guessing that the starter is drawing high amps which causes the amps to the unit to drop during startup. Would using dual 12V batteries solve this problem? 

Yes, using a dedicated 12v battery would solve this problem but it's just a bandied. Running livewells, pumps, 3 graphs and a PP on my 31g cranking battery /w each unit ran on it's own wiring to the battery gives me zero issues. Voltage drops like yours is usually bad, faulty, or too small or wiring or your battery is too small or going bad.