After a longer than usual period of inactivity I recently made it back to my boat and discovered that the batteries did not have enough charge in them to start the engine. Fortunately it's a rather old donk and I can manually crank start it so I did this and left it running for a good 40 minutes. Turned it off and attempted to start the engine using battery power again. Still not enough charge in the battery. I have no solar charging system on board.

The batteries are quite old so I am happy to accept that they are at the end of their life and need replacing.

My question is this - before I go buying new batteries is there a simple test I can perform that confirms that the problem is with the batteries and not some other issue that has coincidentally popped up at this time?

Mat-Try this as a quick way to identify if the batteries are not getting any charge, if you're like me and not real good on multi meters etc.
Being a chippy, I reckon a three inch nail fixes everything!

With the batteries well down,the engine should be well loaded up if the alternator is working properly.
If the engine is spinning freely then its' probably not charging up.

For instance on our little 18hp Volvo, if I run it on say battery 1(fresh starter) and then flick the switch to battery 2(discharged house) the engine will drop about 800 revs because it is working hard to charge the discharged house battery.
As Paleface says, little charge is to be gained at idle speed and around 1500 rpm at least, is a good range for most engines as optimum charging.
Have a good look at the terminals and spades at the alternator as well for good connection.

Other than that, you can take the batteries out of the boat to your local battery guy for some testing.

Cheers C.R.

Thanks for the suggestions guys. I hope to make it out to the boat on the weekend and I will give these tests a try and see what it reveals.

Very neat whiteout, well done!

If it was me I would check the charge rate with a multimeter (you can buy basic ones for not much money and they are a handy tool to have onboard and ashore) to make sure the alternator is charging and if the batteries are more that 3 or 4 years old replace them

A good quality smart battery charger may breath some life into a old battery more effectively than the alternator can but 3 or 4 years out of a battery is a decent life

Regards Don

You could also check your battery terminals would not hurt to give them a clean even if you buy a new start battery clean the terminals before you fit the new battery.
Can you hear the start solenoid (click) when you try to turn the motor over using your battery = could mean low charge or dirty terminals 90% of the time low charge or cell damage
With no multi meter I some times feel the terminals for heat after or while trying to start a motor, any heat = resistance = clean terminals
In my car if Ive any corrosion on the terminals I boil up some water and pour it over the terminals (quick clean)
These days as Donk has already stated battery life three to five years depending on how you keep the charge up

SirJman said..
Very neat whiteout, well done!

We all want to see your wiring job on those GPS parts you just bought SirJman

Mat-I installed Federal GelTech batteries in 2003 and they are still going strong.


Expensive at the time, but they have really paid for themselves. There is no solar or any other charging methods except from the engine.