Jump to content

Marine batteries and dual battery setups


Recommended Posts

Hi raiders,

Yesterday I went out and had a problem where my motor wouldn't start. Normally when I turn the key, the fuel gauge etc would switch on.

However, after fishing a few hours with the fish finder on, I couldn't start the motor. I couldn't even tilt the motor up. Luckily, I had a spare battery on my dual battery vsr setup.

Does this sound like a flat battery? I would think that if it were, the fuel gauge would still work when I flick the switch.

Would using the fish finder for a few hours(about 5) without having the motor on cause it to become flat?

After yesterday's scare, I'm thinking about replacing the battery. It's about 10 years old I think.

Thx in advance.

Link to comment
Share on other sites

I would suggest replacing the battery after 10 years, thats a good life for a battery in the marine environment. Running the fishfinder for 5 hours could well have drained it to the limit. I would suggest it's not just flat but is close to dead. Just as well you had the second unit, very important.

Link to comment
Share on other sites

I am an electronics engineer by trade and worked in the automotive industry for 10 years before moving into computer software.

I believe your issue is almost certainly the age of the battery as already suggested by other members.

Without seeing your battery it would be likely to be a minimum of 50 ampere hours.

Your sounder would be lucky to draw 1.2 amps so the basic formula says 5 Hours X 1.2 amps is 6 ampere hours.

Only a poorly charged or dud battery would be flattened by your sounder running for 5 hours.

Most marine batteries can be deep cycled around 700 times before they need to be replaced. That can happen over a short or a long period of time but at either extreme, ( all in 12 months or all over 10 years) other factors come into the mix that reduce the 700 deep cycle ball park figure.

Its all very scientific and complex really and even with the formal training and industry experience I can't keep up with the latest changes in battery technology.

Having said that I do remember the important stuff and the advice given here by the members is very sensible. Replace the battery ( both if they are 10 years old) and get the alternator checked.

and... go you for have a dual battery setup!... phew!



Link to comment
Share on other sites

The voltmeter is an indication that the alternator is doing working and to some degree how well it is working.

Alternators actually generate Alternating Current (AC) and this is subsequently converted to Direct Current (DC) ( between 13 and 14.4 Volts depending on the engine RPM) by the regulator and by diodes inside the alternator.

If one or more of these diodes goes open circuit it will cause an increase in the DC output voltage which can cook your battery and other sensitive electricals. Poor battery terminal or alternator connections caused by corrosion are also a potential cause of higher alternator voltages so make sure they are corrosion free, cleaned and done up tight.

If your Voltmeter reads around 13.0 to 14.4 Volts when the motor is running you can be reasonably confident that all is well. If it reads more a little more , say 15 volts I would confirm everything with an electrical system check because your Voltmeter may not be accurate. If it reads 16 volts or more and used to read 14 Volts then you are in real danger of cooking a battery and things need to be checked out immediately.

The NRMA battery replacement and check suggested by OZ_Brett is a good idea and will give you the confidence that both batteries and the charging system are up to speed.

If it was a car you just used to go to the corner shop I would whip a battery in it and think no more of it but because its your boat and its no fun getting towed back in I would go that one step more and get it checked out with proper test equipment.



Edited by fragmeister
Link to comment
Share on other sites

I think that is a good choice.

Century have always made great batteries and for a long time were at the forefront of battery technology in Australia

making deep cycle batteries not just for automotive and marine applications but also traction batteries for electric

golf carts and forklifts.

I wouldn't rule out that there may be cheaper batteries of equal quality but Century have the track record.



Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...