Battery death

[bonany]

This might sound really stupid.

I left my starter motor on and drained my two numax marine mv26mf 100ah

Batteries to about 4 volts.

Are they completely dead or can I put anything in them to bring them back to life?

I tried charging them for a few hours and got them up to about 10v but it feels like they are going to drop rapidly.

[alan_fincher]

What do you mean by "I left my starter motor on" please ?

 

Usually a starter will only be "on" if you hold a finger on a button, or hold a spring loaded key-switch to one side, which you can't exactly achieve by accident, usually.

[Chris Pink]

It will take a fair few hours to recharge them.

 

What are you charging with?

 

You need to keep charging until they reach 14.4V (28.8V if they are in series) then for a length of time (measuring the current?).

[Guest]

This might sound really stupid.

I left my starter motor on and drained my two numax marine mv26mf 100ah

Batteries to about 4 volts.

Are they completely dead or can I put anything in them to bring them back to life?

I tried charging them for a few hours and got them up to about 10v but it feels like they are going to drop rapidly.

Do you mean you left your ignition key in the ignition on position? Edited April 17, 2013 by The Dog House

[bonany]

Yeah, it's a safety key or whatever but it doesn't spring back so you can leave it on.

My electrics are a bit weird.

 

I'm charging from the engine with an alternator that usually gets me 14.4v going into it.

 

When I'm trying to charge them now it gets up to 13.5v but drops rapidly to about 10.4 when I turn off the engine.

 

So am I to think its not all over?

[bonany]

Yeah, it's a safety key or whatever but it doesn't spring back so you can leave it on.

My electrics are a bit weird.

 

I'm charging from the engine with an alternator that usually gets me 14.4v going into it.

 

When I'm trying to charge them now it gets up to 13.5v but drops rapidly to about 10.4 when I turn off the engine.

 

So am I to think its not all over?

[ditchcrawler]

Yeah, it's a safety key or whatever but it doesn't spring back so you can leave it on.

My electrics are a bit weird.

 

I'm charging from the engine with an alternator that usually gets me 14.4v going into it.

 

When I'm trying to charge them now it gets up to 13.5v but drops rapidly to about 10.4 when I turn off the engine.

 

So am I to think its not all over?

I think you are going to need a mains charger unless you intend to run the engine for 24 hours. It will take a long time to get them back.

[Chris Pink]

if you can get them onto a shore line for 24 hours, it does sound like you haven't charged them yet. But it is impossible to tell until you do whether they've had it or not.

 

If they were old anyway, this might have killed them off

[alan_fincher]

Yeah, it's a safety key or whatever but it doesn't spring back so you can leave it on.

My electrics are a bit weird.

 

I'm still unclear if you actually managed to leave the starter motor running, and if so whether it started the engine?

 

I would have thought it very hard to not realise it was running?

 

If you just mean it was left in the "ignition on and energised" position, (usually with a red alternator light), that shouldn't matter much, and certainly not discharge the batteries as you have said.

 

Are these two 12 volt starter batteries parallel connected, or have you somehow managed to drain leisure batter/batteries too?

[Chris Pink]

If you just mean it was left in the "ignition on and energised" position, (usually with a red alternator light), that shouldn't matter much, and certainly not discharge the batteries as you have said.

 

depends how long, I have done this in the past (and had a fair old job getting the alternator to go again)

 

to the OP: when you are running the engine now is the alternator warning light going out?

[magnetman]

one of my boats has an electric circulation pump for the engine cooling from the skin tank. this comes on when you turn the key before the starter. its a bit unusual but very reliable and effective. if the key is left in it flattens the battery quite quickly.

[alan_fincher]

depends how long, I have done this in the past (and had a fair old job getting the alternator to go again)

 

to the OP: when you are running the engine now is the alternator warning light going out?

I must be quite lucky then, as I have managed to do it for sometimes lots of hours hours, and on multiple occasions, never so far with any obvious detrimental effect.

[magnetman]

one of my boats has an electric circulation pump for the engine cooling from the skin tank. this comes on when you turn the key before the starter. its a bit unusual but very reliable and effective. if the key is left in it flattens the battery quite quickly.

 

 

Yeah, it's a safety key or whatever but it doesn't spring back so you can leave it on.

My electrics are a bit weird.

 

I'm charging from the engine with an alternator that usually gets me 14.4v going into it.

 

When I'm trying to charge them now it gets up to 13.5v but drops rapidly to about 10.4 when I turn off the engine.

 

So am I to think its not all over?

have you got two seperate sets of batteries? I can't see how you can start the engine again with 10.4v at the battery ?

[bonany]

I must point out that my system is very basic.

I start the lister engine with the crank arm.

But to get the charging system to work I have to switch the starter motor safety switch on.

I have no warning lights on the alternator.

 

I know, it's pretty weird. I don't get it really.

[ditchcrawler]

I must point out that my system is very basic.

I start the lister engine with the crank arm.

But to get the charging system to work I have to switch the starter motor safety switch on.

I have no warning lights on the alternator.

 

I know, it's pretty weird. I don't get it really.

OK so you left the batteries connected for some time and flattened them. I don't think you have a hope in getting them back on the engine alternator not unless yoy go for a couple of 12 hour cruises with decent engine revs as I am guessing you only have a small alternator on a relativly slow reving engine

[Arthur Brown]

You really need to get the batteries to a mains charger, put in their capacity in amp hours, and see how they fare.

 

An alternator without a warning light may not even be generating anything.

[bonany]

Thanks for all your help guys.