When is the time to ditch my batteries?

[nb celestine]

A couple of weeks ago I charged my 4x 110,s up to float with my gennie and charger. I don't do this as often as I should. Lets say every time I get the hoover out.

About once a month!!

Anyway, after leaving them for about an hour, I tested them with the hydrometer and every cell was showing roughly 1.22. On my hydrometer scale it is just into the fair category.

My questions are this.

 

Can you tell by the hydrometer readings how far the capacity has diminished?

And if so, where does the cut off point come where it isn't cost effective to keep charging sulphated batteries?

 

They are 2 year old liveaboards, by the way. Ta.

[Tony Brooks]

Remember float often does not mean fully charged so do not expect 12.80 to 1.300, but I would say there is a lot of sulphur locked up in sulphate. The cut off point is when they no longer hold enough charge for your usage.

[Naughty Cal]

When they start to let you down is the time to change them.

 

If they are still coping with your demands then leave them for now but when they start to become unreliable is the time to change them.

[blackrose]

I was pondering the same question. My batteries are 8 years old, although much of their long life has been on float charge. Although their a/h capacity is less than half of what it was originally, the batteries still perform well with my low loads and occasional higher loads from the inverter.

 

Away from shorepower and charging, the volts never drop when the boat is left for a few days and the 8 year old BT batteries still seem fine too. Is there any point in renewing them?

Edited May 23, 2013 by blackrose

[Naughty Cal]

I was pondering the same question. My batteries are 8 years although much of their long life has been on float charge. Although their a/h capacity is less than half of what it was originally, the batteries still perform well with my low loads and occasional higher loads from the inverter.

 

Away from shorepower and charging, the volts never drop when the boat is left for a few days and the 8 year old BT batteries still seem fine too. Is there any point in renewing them?

No.

 

If they are adequate for your power demands then leave them be.

 

When they start to let you down its time to replace them.

[magnetman]

I was pondering the same question. My batteries are 8 years although much of their long life has been on float charge. Although their a/h capacity is less than half of what it was originally, the batteries still perform well with my low loads and occasional higher loads from the inverter.

 

Away from shorepower and charging, the volts never drop when the boat is left for a few days and the 8 year old BT batteries still seem fine too. Is there any point in renewing them?

out of interet Mike how do you know they are less than half their original a/h capacity ? Edited May 23, 2013 by magnetman

[blackrose]

out of interet Mike how do you know they are less than half their original a/h capacity ?

 

From 100% SoC (supposedly 405a/h), I switched the charger off and left my fridge on AC from the inverter drawing exactly 10 amps (at 12v measured on the battery monitors) while I was out for the day. No other power was being drawn.

 

When I returnbed 10 hours later I would have expected to see the batteries at around 75% SoC or 300 a/h according to the Smartgauge and my other battery monitor, but both showed about 50%, which indicates to me that they don't actually hold 405 a/h when fully charged anymore and it's probably more like 200 a/h.

 

Have I got that right?

Edited May 23, 2013 by blackrose

[ditchcrawler]

Whatever sort of fridge have you got to draw that sort of load.?

[alan_fincher]

Whatever sort of fridge have you got to draw that sort of load.?

A Gas/240V/12V "Three Way" absorption type, by the sound of it!

[ditchcrawler]

A Gas/240V/12V "Three Way" absorption type, by the sound of it!

I thought on 240 volt even they had thermostats so wouldn't be on constantly, if so his batteries may be even worse than he thinks

[Trento]

My cheapo Asda fridge draws 0.3A ac for 4A DC from the inverter (24v) and is on for 8 mins 3 times per hour +/-.

 

Is this OK, the batteries don't seem to notice the discharge much..

[magnetman]

sounds quite high to me

 

4a at 24v is 8a 12v

 

mine uses about 30ah at 12v

 

 

I make it ~77ah 12v equivalent for the one just mentioned

Edited May 23, 2013 by magnetman

[ditchcrawler]

sounds quite high to me

 

4a at 24v is 8a 12v

 

x 0.5 approx 4x24 is 96ah per day 12v equivalent

 

mine uses about 30ah at 12v

 

a bit less than 96 because 3 x 8 is 24 mins not.30 mins

 

I make it ~77ah 12v equivalent

mine uses 7 amps for 6 hrs a day that is a Lec,with fans in the floor and extra insulation on the sides. As supplied it was 8 hrs a day

[blackrose]

Whatever sort of fridge have you got to draw that sort of load.?

 

A gas fridge. Low electricity consumption is not its forte. It's about 1amp to run the inverter, so the fridge is about 9amps.

 

I thought on 240 volt even they had thermostats so wouldn't be on constantly, if so his batteries may be even worse than he thinks

 

No they won't be, because I only ever have the fridge on AC when I'm on shore power (apart from that test).

Edited May 23, 2013 by blackrose

[ditchcrawler]

 

 

 

 

No they won't be, because I only ever have the fridge on AC when I'm on shore power (apart from that test).

That is not quite what I meant. You said the fridge was on for i think 10 hours and worked out how much power had been used on those figures. My point was that if it has the thermostat it may have only been run for 5 hrs. so you have only used half as much power as you think and therefore your batteries are in a poorer state than you thought.

[bottle]

Blackrose

 

I may have got this wrong but just to clarify.

 

Are you running the fridge (three way) on 12v dc? (for the test)

[nb Innisfree]

FWIW I fixed up a timer to log the amount of time the t/stat switched in. I did several tests in winter and summer, result:- 12 hours running per day winter and summer (16 ah @ 24v per day-130 litres capacity) Seemed a bit odd at first but considering our boat had the same internal temperature in both of those seasons it makes sense.

[nb Innisfree]

A couple of weeks ago I charged my 4x 110,s up to float with my gennie and charger. I don't do this as often as I should. Lets say every time I get the hoover out.

About once a month!!

Anyway, after leaving them for about an hour, I tested them with the hydrometer and every cell was showing roughly 1.22. On my hydrometer scale it is just into the fair category.

My questions are this.

 

Can you tell by the hydrometer readings how far the capacity has diminished?

And if so, where does the cut off point come where it isn't cost effective to keep charging sulphated batteries?

 

They are 2 year old liveaboards, by the way. Ta.

Time to renew when fuel usage for charging becomes uneconomical and/or charging times become unsociable, that depends on fuel costs set against the cost of new batt.

 

Some calculator bashing and a wet finger in the wind.

[blackrose]

That is not quite what I meant. You said the fridge was on for i think 10 hours and worked out how much power had been used on those figures. My point was that if it has the thermostat it may have only been run for 5 hrs. so you have only used half as much power as you think and therefore your batteries are in a poorer state than you thought.

 

I see. I might be wrong but I don't think it has a thermostat - it just runs constantly? Or perhaps that's just on 12v and gas?

 

Anyway, if they are worse than I thought they're still ok. I can often go 3 or 4 days without charging them, staying above 50% on the Smartgauge (even though it may be wrong), and the BT batteries never ran out of power over the 5 weeks I moved the boat from Windsor to Bidford on Avon (via Bristol).

 

Blackrose

 

I may have got this wrong but just to clarify.

 

Are you running the fridge (three way) on 12v dc? (for the test)

 

No, on 240v from the inverter.

Edited May 23, 2013 by blackrose

[bottle]

I believe it is only 12v dc that is not thermostatically controlled.

 

The control (knobs) if you have them will be the thermostat controls, there will be one for gas and one for 240v dc.

 

This may depend on model and the age of the fridge.