Yesterday at the tail end of my morning fishing trip my Helix 5 SI sonar began occasionally shutting itself off. Just out of the blue. I found that I couldn't just turn it back on, but if I removed the power cable and then plugged it back in, it would turn on again. When it'd turn on then, it would only load half of the info bar on the left side (the bottom half- time/gps coords would just be blank) and if I scrolled to GPS view it would say it couldn't get a position fix. After a minute or so it'd get it and work fine for maybe 5 minutes, then shut off.

I took the battery out that I'd been using (it's only powering the sonar) and tested the voltage and it was 11.67. I had fully charged it a few days before the trip. Humminbird says the unit will not work at voltage under 10.8 volts, which I am well above.

Does anyone have any suggestions or knowledge what caused this? I will charge the battery and see if that changes it but in the meantime I'd be interested to know if anyone else has had this problem.

if you hook it up to a fully charged battery, does the problem go away?

My Helix 7 would shut off if I shared the battery with my stronger trolling motor (and it's possible that battery is weak)

I'm sure Wayne may be able to give you a better answer than what I am about to guess but Humminbird stating that the unit will not work with voltage under 10.8 may be referring to, sometimes, when you crank your big motor the voltage will drop down into the 11.6 (ish) or even lower range when cranking and then immediately return to normal voltage. If you are cranking your motor and the voltage drops below 10.8,  the unit will shut off. I've never had my battery drop below 11 when cranking my big motor. Just going by 12v battery voltage charts, 11.67 is considered 20% and I'm guessing that due to the load on the battery from the electronics and it being so low, it's shutting down. Charge your battery. If you charged your battery days prior to going out and then it read 11.67 when you plugged in the unit, your battery is toast. It should still read full or close to it. 

Thanks for weighing in fellas. I should also have pointed out that the unit is running on its own battery. That battery is powering nothing else.

I'll charge it up and see if it still happens. That'll be the real acid test.