Humminbird 997 Power Supply

After hooking up my 997 and setting the low battery alarm to 12 volts, I thought that I had a battery going bad. It was only registering 12 volts when fully charged on the 997 screeen. I got my voltmeter out and it said 12.6 volts. The 997 manual recommends using 18 gauge wire to run to the battery. The problem with this is that the graph reads about .5 to .6 volts lower than the actual battery is. I've tried hooking the 997 unit up to about 4 different batteries and they are all reading about the .5 to .6 volts lower than the voltmeter. A buddy of mine who has last year's model of the Humminbird unit said that he had the same problem until he changed to a bigger gauge wire running to the battery. Just wondering since I know that it's reading about .5 volts low, will it be ok to leave the 18 gauge wire hooked up or will it cause other problems?

I believe you are fine as is. The specs (as stated by Humminbird) is 10 to 20 volts dc. 18 gage wire can easily handle the current required to operate the 997. I have 797, but they both have same power specifications. Be sure not to run it on the TM battery.

Internally, the units microprocessor reads the dc voltages via a a/d converter and does voltage conversions, similiar to your digital volt/ohm meter. It is probably not as accurate as your VOM, as it is just a ball park reading and not system critical. I am guessing at all this, but I'll put money on it that I am guessing good here. ha

A 5% voltage drop is acceptable with most gear.