Engine battery...how long does it last?

[Iain C]

I have a fairly standard setup on my boat. Engine battery/service battery. Off/1/2/both switch. Lombardini M602 16hp with a standard alternator...no clever charging, I have a Forgen generator but it's croc clipped to the service battery only. Boat lives on a swinging mooring so never gets plugged in...I've owned her for four years and she's only been out for the winter once (I prefer to keep sailing!) and the batteries stayed on board.

I have replaced the service battery twice, and TBH it's probably not far off needing a new one. However...the engine battery is the original. Off the top of my head, I don't know the Ah or age of the battery, but I reckon it must be at least 10 years old, possibly even 15, but starts the engine first time every time.

Am I on borrowed time here or is this a case of "they don't make them like they used to" and these things can go on for ever?

 

[nigelmercier]

I would replace it after 10 years, mine died at an inconvenient moment after 12.

 

[temptress]

....
I have replaced the service battery twice, and TBH it's probably not far off needing a new one. However...the engine battery is the original. Off the top of my head, I don't know the Ah or age of the battery, but I reckon it must be at least 10 years old, possibly even 15, but starts the engine first time every time.

Am I on borrowed time here or is this a case of "they don't make them like they used to" and these things can go on for ever?

Not as simple as that. What are the batteries? tType/Construction/Ratings/ages; Why is the domestic side failing? What type of batteries do you have? Can you check the cells in each one? You could do a load test on the engine battery by way of a test? How do you usually charge the engine battery?

Your engine battery is probably OK. But on theother hand it may not be. I think a bit more investigatin is required. However it is unlikely to fail 'instantly' and should give you soem indication of trouble such before it fails.

 

[Bilgediver]

I have a fairly standard setup on my boat. Engine battery/service battery. Off/1/2/both switch. Lombardini M602 16hp with a standard alternator...no clever charging, I have a Forgen generator but it's croc clipped to the service battery only. Boat lives on a swinging mooring so never gets plugged in...I've owned her for four years and she's only been out for the winter once (I prefer to keep sailing!) and the batteries stayed on board.

I have replaced the service battery twice, and TBH it's probably not far off needing a new one. However...the engine battery is the original. Off the top of my head, I don't know the Ah or age of the battery, but I reckon it must be at least 10 years old, possibly even 15, but starts the engine first time every time.

Am I on borrowed time here or is this a case of "they don't make them like they used to" and these things can go on for ever?

Might start the engine once!!! How many times would it try if something wasn t right? Try the starter battery on the house system and see how long it manages

 

[charles_reed]

I would replace it after 10 years, mine died at an inconvenient moment after 12.

As a rough rule-of-thumb I agree.

However I don't have a dedicated engine battery...

 

[charles_reed]

I would replace it after 10 years, mine died at an inconvenient moment after 12.

As a rough rule-of-thumb I agree.

However I don't have a dedicated engine battery...

 

[Sailingsaves]

Buy an hydrometer and check the battery. Also check it with multimeter. If you return to your boat on a cold day and Voltage is 12.7V and hydrometer readings are good, then start looking after the battery and fit a 5W solar panel (£20) to keep it topped up whilst away from boat. Just wire solar panel up - no tricky things required at such a low wattage.

If voltage is below 12.1 and hydrometer readings are poor, replace battery and fit solar panel.

But if you buy a bigger panel and connect it to all batteries then you need to do a little more wiring; might work out best in the long run and good batteries will remain good for many years.

My car battery is still going strong after 20 years, but I have looked after it.

On a fulltime swinging mooring I would definitely look to use free renewable energy to keep my batteries in tip top condition.

I have a fairly standard setup on my boat. Engine battery/service battery. Off/1/2/both switch. Lombardini M602 16hp with a standard alternator...no clever charging, I have a Forgen generator but it's croc clipped to the service battery only. Boat lives on a swinging mooring so never gets plugged in...I've owned her for four years and she's only been out for the winter once (I prefer to keep sailing!) and the batteries stayed on board.

I have replaced the service battery twice, and TBH it's probably not far off needing a new one. However...the engine battery is the original. Off the top of my head, I don't know the Ah or age of the battery, but I reckon it must be at least 10 years old, possibly even 15, but starts the engine first time every time.

Am I on borrowed time here or is this a case of "they don't make them like they used to" and these things can go on for ever?

 

[jac]

Might want to consider how you use the domestic.

I assume with that set up that you switch to both when starting and running the engine then switch to domestic only when the engine goes off.

If that is the case, then potentially you are using both to actually start.

Secondly, if the engine start is a decent size and engine is well maintained, clean fuel etc then you are probably taking very little out of the engine start each time but then finding that it soon gets recharged to it's maximum. 30 mins of engine running will probably easily put back all the power that was taken out to start, even if charging both banks.

In contrast, if the domestic is only getting say a 30 minute charge twice a day as you motor in and out then how much are you putting back. You don't say how big the alternator is so the charge in could be anything and again not sure what output you are getting from your forgen, but what is your discharge and how big is the domestic bank.

If we assume that in the absence of sophisticated chargers that you are only getting your domestic battery to 80-85% of nominal capacity by Friday, then over the weekend you may be discharging to way below 50% which will dramatically reduce the number of cycles you can put the batteries through.

My suggestion would be:
Reduce consumption - electrical items off or switch to LED etc.
Increase Battery capacity - same ah discharge will do less damage to bigger bank.
Investigate proper traction batteries - designed for domestic type loads.
Increase charging from the engine - either by bigger alternator or the "clever charging kit"
Increase charging from solar/ wind.

You need to be in a position where the amount you take each day won't discharge your batteries below 50% ideally and then have the capacity to get it fully charged each day. On passage or on a cruise you may have to settle for 85% as full but if the solar/ wind can top you back up to 100% when the boat is unattended then your domestic bank will have a long and happy life.

 

[Stemar]

This spring I had to replace my starter battery. It had been there for the best part of 10 years and was second hand when I got it.

Provided your domestic battery is up to starting the engine, you have a fail safe system, so I wouldn't be too concerned but, if your second domestic battery in 4 years is on its last legs, I reckon there's a need to do something about that.

I'm in a similar situation to you, swinging mooring, no external charging, afloat all year most years. Last year I fitted 40w of solar panels and a dual battery controller and, even in winter, both batteries are well up to 13+ volts when I arrive. During the summer, apart from our rather inefficient cold box, the panels could keep up with our leccy use at anchor. I'd suggest that a similar setup could be the kindest thing you could do for your batteries.

 

[Iain C]

Thanks for the replies. So it sounds like the engine battery can last that long but it might be prudent to replace it soon.

WRT the domestic battery, it does get a bit of a kicking. 12v coolbox, cabin lights, eberspacher, nav lights, VHF, AIS, GPS, Navtex, wind instruments, log, echo sounder, GPS repeaters and the autohelm, as well as a waterproof iPad constantly on charge will all take their toll,and it's often been cycled down to 0% according to the BM1. I've not done the maths but face it, there's almost no point...it won't be a pretty answer! This year I have swapped the cabin lights, tric and anchor light for LEDs and the camping coolbox for a Waeco unit, but on the project list next year is second battery and solar charging.

Thanks again.