Boat's electrical power

[WallyGator12000]

So I've got a quick question...my 2002 ranger has 3 batteries, two deep cycle and 1 cranking. I noticed last night that when I moved the motor tilt up and down, or started the motor, the lights would flicker. Twice my console locator even turned off and on (from lack of power).

I made sure the batteries were charged this morning, and the dash lights would still flicker as I put the trim up and down in the garage on a quick check. Does this mean one of my batteries is going bad/won't hold a charge? I am planning on taking it in to get all three of the batteries load tested, but I guess I'm a little confused. This is because I was assuming that my 125 Merc's alternator would charge the cranking battery, and the on-board charger would charge the two deep cycles. I just bought the boat this summer, and I haven't rigged the batteries myself, but I would have assumed the locators would not be rigged to the cranking battery, and instead to the deep cycle.

Any ideas?

[DaMoose]

First off, do you have a 24V trolling motor? If you do I would say that the 2 deep cylces are hooked to that. All lights and electronics are more than likely hooked up to the cranking battery, this is how my boat is wired.

[WallyGator12000]

Yeah, I do have a 24 volt trolling motor, I didn't realize that the two deep cycles would be all that are hooked up to that. So, both my locators are hooked up to my cranking battery, and I likely either have a bad battery or a bad alternator?

Thanks for the help!

[Ralph Wiggum]

It's pretty common to have your trolling motor hooked to a different power source than everything else. This helps to eliminate electrical interference from the trolling motor on sonars and radios and such.

[swampbuck]

Even though your main engine will recharge your starting battery running pumps, radio electronics puts a drain on the starting battery.

It is a good idea to throw a charger on it at least once a week if you use it a lot.

Nothing worse than a dead battery

[marine_man]

Everyone's spot on here... all your accessories run off your starting battery. Any idea how old your batteries are? Your starting battery might be nearing the end of it's life.

The charging system on your Mercury 125 motor is a rectifier, and doesn't output significant amperage to charge unless you're above 1/2 throttle... so if you're not doing much running beyond 1/2 throttle you're not getting much charging.

If you'd like to see this first hand... connect a multi meter to your battery and observe the voltage with the motor off. Then, start your motor, and slowly increase the throttle, and watch the voltage rise. At full throttle you should be seeing somewhere above 13 volts.

marine_man

[WallyGator12000]

Thanks for the help guys, I went and had my cranking battery load tested, and it was bad. Not a cheap fix, but a fix nonetheless!