How long can a starting battery sit?

[Chotu]

Every discussion on here is always about the house bank. Did you ever notice that?

Boy do I know my way around a house bank.

I have a question about starting batteries.

my outboard starting batteries have been sitting for I suppose three years? They were working fine when they started sitting.

they are an island onto themselves. They are not attached to the main electrical system in any way.

so how long do you think these can last just sitting there? Do you think it’s a reasonably good assumption that they will charge up from the outboards and still work if I jump start them?

[ChrisJHC]

You might be better with a trickle charger rather than jump starting.
Slow and steady should bring them back better.
Still no guarantees of course!

[Chotu]

Originally Posted by ChrisJHC

You might be better with a trickle charger rather than jump starting.
Slow and steady should bring them back better.
Still no guarantees of course!

OK. Sounds reasonable. What about just letting the engine charge it as you motor though? That’s a trickle charge, yes?

[pcmm]

Originally Posted by Chotu

OK. Sounds reasonable. What about just letting the engine charge it as you motor though? That’s a trickle charge, yes?

whether or not its a trickle charge from the Outboards will depend on their charging output. If you put the batteries away 3 years ago and they are conventional FLA then they probably have a low level of charge left and Sulfation may begin to come into play. Get them charged ASAP Even the outboards output will be better than nothing, but I would run and charge them all the way back to full, don't partially charge them at this point.

[rslifkin]

Sitting for 3 years without being charged at all, I'd expect them to have self discharged enough to sulfate and become junk. Particularly for flooded batteries.

Generally, I don't like to let any battery sit for more than about a month without some charging to keep it topped off.

[Wotname]

Depends on the battery. Odyssey AGMs state they loose only 3% of capacity after 12 months of sitting unused.
Also depends on ambient temperatures - hot is bad.

[Mike OReilly]

Impossible to say for sure. Depends on type of battery, state of battery, location, and probably the whims of battery angels and demons.

All I can tell you is, I left my starter (and house) battery alone and unattended for 33 months. When I came back to the boat it measured 12.5v before any loads were added. I got it fully charged and it has performed just fine all season (as has the house bank).

I'm in Newfoundland. It's cold for 1/2 the year, but not deeply cold. And for the other 1/2 it is pretty warm (hitting over 32ºC this summer many times). The batteries were fully charged and then completely disconnected from all circuits (as in, I took ALL leads off the batteries). No charging was provided for 33 months. These are flooded, maintenance-free batteries.

By all I thought I knew about batteries (mostly gleaned from CF ), these batteries should have been long-dead, but they weren't. So maybe the common wisdom about batteries isn't so true... or perhaps there's a lot more complexity to the question. At this point I don't know what to believe about batteries.

[siamese]

If it was battery, my first step before giving them any charge, would be to check them with a multimeter. If discharged, I'd assume it's been discharged for a long time and replace it.

[valhalla360]

Lead acid batteries are happiest at 100% charge.

After 3yrs, they have likely self discharged quite a bit. What is the voltage reading on them? If you are talking jump start, I assume it's not a good sign.

From here out, it's likely a carp shoot. They may or may not take a charge and if they do...They might be fine for a few years. They might fail tomorrow.

I would check the water levels and fill with distilled water. Then put on a low amp charger for a day and see where things are at? This assumes you have a backup means of starting (connect to the house bank, pull start the outboard, etc...) If it's the sole means of starting, I wouldn't mess with them.

Assuming it's a single modestly sized 12v battery, just get a new one. This is likely why you don't see a lot of people wringing their hands over the starting battery. For $75-100 you can have new. A big house battery bank can run several hundred, even thousands of dollars, so trying to save it is far more useful.

[PaulCrawhorn]

Letting any lead battery just sit for months without topping up is abusive and will drastically shorten useful lifespan.

Years fuggedaboudit

If their reliability is critical to your use case, just replace them now with new, and resolve to take better care of them.

[MicHughV]

Only one way to find out.
Charge 'em up best you can and see if they will hold the charge.
I tend to agree with above, that after 3 years with no charge, they will likely be duds.
Prior to charging you might want to check the fluid level in the bats.
I got $10 sez they are likely dry as a bone.

[smac999]

those batteries are going to be toast. what's the voltage? 0v I bet. they should have be fully charged every couple months. or left on a battery tender.

[PaulCrawhorn]

Yes I meant topping up in both senses for FLA units

[deblen]

My FLA's(house-deep cycle,start-common auto/truck)sit for 6 mos Nov thru Apr,aboard the boat,Neg wires disconnected,about same climate as NFLD. Have done this for 14yrs.
In Apr,they read 12.5. I hook up the Neg cables,start the engine & go.
They do get "grunty" at 5yrs old.
I replace them with like bats.
Works for me.
I also find that my road vehicle batteries work about the same way-except they get used year round.
Cheers/Len

[Sailmonkey]

Originally Posted by Chotu

OK. Sounds reasonable. What about just letting the engine charge it as you motor though? That’s a trickle charge, yes?

The engines are not meant to charge a battery, more to maintain one.

Either way, if these batteries have been sitting three years unattended and they’re dead now (what is the resting voltage if any) they’re toast. Like other posters have said, sulphation has done its work.