Old battery or other problem

[Macdoug]

Over the last few weeks I have noticed that it has been increasingly hard to start my boat. It seems like a classic case of dying battery. I use my boat about once a week, and each weekend it sounds like it is struggling to turn the starter motor more and more, until this weekend it barely started at all. However having run the engine for a bit (and so charge the battery), it starts fine when I restart several hours later to dock. I assume that the alternator is running ok as it does charge the battery when engine is running and house batteries are good, and the battery currents when running the engine are as expected.

So I took the battery out this weekend after sailing and trickled charged it at home. My relatively cheap trickle charger said it was fully charged within an hour (I must admit that I ran the engine for all but the time I was at anchor so about 3hours). .I took it to a car shop who tested it including a load test and said it was fine. When I checked voltage I am getting 13.05 v.

I have no idea how old the battery is as it came with the boat, but looking at the price sticker on it and how much they cost now, it must be a few years old. It is plenty big enough for the engine at 720 cca.

So is it a dying battery that just manages to pass a load test because it has been charged up until about 8 hours before the test, or is something else wrong?

I am perplexed because I was sure about the problem. Not yet bought a new battery as shop who had them in stock said I didn’t need it.

Thanks.

[Searles]

Check your starter motor brushes and connections ,are the cables getting warm to hot ,how old are the cables ,may not be the battery .⛵️⚓️

[Macdoug]

Cables only a few years old. Changed when the house battery bank was upgraded before I bought the boat about 3 or 4 years ago. Connections are all good. Will check starter motor brushes. I assume these are original so 9 years old.