---

I have a 1987 Montauk. I would like to mount a bow mount Minn Kota Powerdrive 24 V trolling motor. My current battery in the boat is in the rear so I will add 2 new batteries in the console (hole cut in console floor). My 1987 Mercury 70 HP outboard does not have a voltage regulator and my Raymarine Dragonfly GPS /sonar turns off when I am above 2500 rpm's. The sonar GPS has a cutoff above 15.6 Volts. I thought I could tap one of the new 12V batteries to power the sonar GPS. I read that I should not share the same battery system for the GPS/sonar as the trolling motor because of electrical interference from the speed controller of the trolling motor. My other option is adding a voltage regulator to the existing power supply from the current wiring to the GPS/sonar. Does anyone have an experience with this that can chime in?

---

If fixing the motor charging system is not an easy option, I would add an additional battery just for the electronics. It would not need to be very large, an ATV or motorcycle battery would probably work. The trolling motor batteries need to just power the trolling motor. MinnKota sells 3 and 4 bank chargers so each battery on the boat could be charged at the same time.

---

I am not familiar with your motor but I always thought that the voltage regulator was used with a generator and alternators have an integral regulator. If you have unabated current from your charging system you will ultimately cook your battery. Do square away your charging system. Those dc wires can melt/fry in a second. The Blue Sea dual battery plus charging system has a battery isolation feature. Electronics should be independent of any potential spiking or surging or you can ruin them.

---

Back in 1987 Mercury only used a rectifier to convert the AC to DC. In 1988 they added a regulator. Back in 1987 flooded lead acid batteries with fill caps were the norm. As the battery overcharges during higher rpm operation some of the water in the battery boils off. You just need to periodically add some water to the battery to replace what was lost or risk killing the battery. It's actually a pretty reliable system with only a rectifier used to convert the AC to DC. The charging system is functioning as designed. There is a company that makes a rectifier with a regulator that some people retrofit for use on these older engines.

---

I was reflecting a bit about the charging system of your motor. 1987 motor technology might not be compatible with today's electronics. If you are wanting to use current sophisticated gps/fishfinder/sonar you may want to talk with the manufacturers of the equipment to see what they have to say. Possibly Blue Sea to see if their dual battery isolation system would work in your situation.