Do I need new house batteries ?

[simonfraser]

2x Hankook SV AGM 110Ah, bit over 4 yrs old
never run down to less than 60% capacity according to shunt, always shore charged straight after use
Just pulled 55Ah out, cabin heater fridge few LED lights, over 18 hours

voltage on shunt 12.2V just before attempting to start the diesel Hob, not (no useful Solar this am)
needs 12.4V

started Hob with OB running, 13.0V straight away, left OB running 10 mins
voltage on shunt hour later 12.3V

in the past I have run heater OR fridge overnight, no problem

Q, am I overstressing the existing set up, or are the AGM’s up for replacement ?

tnx

 

[Stemar]

I expect LA leisure batteries to last longer than four years, and AGM should do better than LA. You pulled half their capacity out of them, probably a bit more considering they're not brand new. A quick google gave this table for AGM batteries under no load conditions

SOC(State of Charge)	OCV(Open-Circuit Voltage)
100%	12.85V
75%	12.55V
50%	12.25V
25%	11.95V
0%	11.65V

which suggests you're there or thereabouts, I reckon they're probably OK, but I wouldn't want to take 'em any lower and. if practicable, I'd look to add capacity. Someone will be along in a minute to explain why it isn't a good idea to add a new battery to an old bank, but...

 

[PaulRainbow]

I expect LA leisure batteries to last longer than four years, and AGM should do better than LA. You pulled half their capacity out of them, probably a bit more considering they're not brand new. A quick google gave this table for AGM batteries under no load conditions

You forgot that the OP has 2x100ah batteries Steve, so only 25% of the theoretical capacity.

 

[PaulRainbow]

2x Hankook SV AGM 110Ah, bit over 4 yrs old
never run down to less than 60% capacity according to shunt, always shore charged straight after use
Just pulled 55Ah out, cabin heater fridge few LED lights, over 18 hours

voltage on shunt 12.2V just before attempting to start the diesel Hob, not (no useful Solar this am)
needs 12.4V

started Hob with OB running, 13.0V straight away, left OB running 10 mins
voltage on shunt hour later 12.3V

in the past I have run heater OR fridge overnight, no problem

Q, am I overstressing the existing set up, or are the AGM’s up for replacement ?

tnx

I'd do a drop test on each battery.

1. Fully charge the batteries isolate and leave to rest for a while.
2. Note voltage.
3. Apply a known load (headlamp bulb is commonly used for this), for an hour.
4. Remove load, leave for a while, note voltage.

Repeat 3 and 4 until you get to 50% discharged. You can then work out exactly what the usable capacity is.

 

[simonfraser]

Tnx guys, and 5C, so 80% of theoretical max
And as said older, so prob more like 150 Ah for the 2

rather than the theoretical max 220 Ah

Which would fit in with the 12.2 (which was under light load)

Ok, cant fit more AGM in with the tools i think i need

I'll reset the battery capacity on the shunt and monitor the voltage and see if it drops more when colder again

4x 6V trojan will fit

Tnx, always helpful to ask / think

 

[PaulRainbow]

Tnx guys, and 5C, so 80% of theoretical max
And as said older, so prob more like 150 Ah for the 2

rather than the theoretical max 220 Ah

Which would fit in with the 12.2 (which was under light load)

Ok, cant fit more AGM in with the tools i think i need

I'll reset the battery capacity on the shunt and monitor the voltage and see if it drops more when colder again

4x 6V trojan will fit

Tnx, always helpful to ask / think

If you need to replace, 4 x T105s would be a good move Simon.

 

[simonfraser]

12.4 no load 30 min rest
Started hob 7A draw
Down to 11.4 - failed to start

Was that a sufficient load test to show they're on the way out

 

[PaulRainbow]

12.4 no load 30 min rest
Started hob 7A draw
Down to 11.4 - failed to start

Was that a sufficient load test to show they're on the way out

What hob ?
How are you powering the hob ?
If an inverter, which one, what size cables ?
What was the battery voltage after 15 mins with no load, no charging ?

 

[simonfraser]

Diesel hob, see above

 

[PaulRainbow]

Diesel hob, see above

Sorry Simon, missed that.

Something certainly doesn't look right there, i would double check the batteries as per post #4 to be sure.

 

[Stemar]

You forgot that the OP has 2x100ah batteries Steve, so only 25% of the theoretical capacity.

Oops

 

[B27]

2x Hankook SV AGM 110Ah, bit over 4 yrs old
never run down to less than 60% capacity according to shunt, always shore charged straight after use
Just pulled 55Ah out, cabin heater fridge few LED lights, over 18 hours

voltage on shunt 12.2V just before attempting to start the diesel Hob, not (no useful Solar this am)
needs 12.4V

started Hob with OB running, 13.0V straight away, left OB running 10 mins
voltage on shunt hour later 12.3V

in the past I have run heater OR fridge overnight, no problem

Q, am I overstressing the existing set up, or are the AGM’s up for replacement ?

tnx

Your outboard is not doing much charging?