What to expect from my batteries

[Daydream believer]

Ok here goes for the prize for the one millionth battery thread
I have 2 domestic agm batteries 90 amp 4-5 years old ( do not remember actual date) I have usual electrics- autopilot instruments nav & int lights but no fridge.
I am worried that they may need replacing for this season so last month I charged them up as usual. Then disconnected them & the V reading was 13.3 Volts.
Today they were both13 V. I want go know if they will work Ok so at 12-00 hours I re connected them & turned enough lights on to show a discharge on the BMA of 2 amps
Within 30 secs they read 12.77 volts
If i go back tomorrow at 12-00 that will be 24 hours * 2 amps = 24 amphours.

If i leave for another 24 hours it should be 48 & so on
So what should i expect to see on the volt meter when i go back tomorrow ( saturday & sunday ( 48 hours) ---apart from a couple of flat batteries & a bill for £squids
How long can I run them at 2 amp & at what point in time do i need to check the voltage & what level should it be on AGM
Thanks

 

[nortada]

4-5 years they have served you will so possibly time to bight on the bullet.

From experience, when they start to go duff, they can go duff very quickly. Moreover, don't be tempted to get just one replacement - again, from bitter experience, the old battery can knacker the new one.

ps I am just about to replace my whole battery bank.???

 

[VicS]

Ok here goes for the prize for the one millionth battery thread
I have 2 domestic agm batteries 90 amp 4-5 years old ( do not remember actual date) I have usual electrics- autopilot instruments nav & int lights but no fridge.
I am worried that they may need replacing for this season so last month I charged them up as usual. Then disconnected them & the V reading was 13.3 Volts.
Today they were both13 V. I want go know if they will work Ok so at 12-00 hours I re connected them & turned enough lights on to show a discharge on the BMA of 2 amps
Within 30 secs they read 12.77 volts
If i go back tomorrow at 12-00 that will be 24 hours * 2 amps = 24 amphours.

If i leave for another 24 hours it should be 48 & so on
So what should i expect to see on the volt meter when i go back tomorrow ( saturday & sunday ( 48 hours) ---apart from a couple of flat batteries & a bill for £squids
How long can I run them at 2 amp & at what point in time do i need to check the voltage & what level should it be on AGM
Thanks

A domestic battery bank consisting of two 90Ah batteries that are 4 or 5 years old .... correct ?

A month or so ago you charged them , When disconnected they then read 13.3 volts. Fair enough. The reading is good not particularly meaningful .

Today, about a month after they were charged and after standing with no further charge they read 13 volts . That is surprising I would have expected less after a month. Probably no more than 12.8, or thereabouts

A 2 amp load dropped the voltage to 12.77 within seconds.... that's fine. First indications are that your batteries are OK but you need to check that they hold their charge
I would, therefore, have then left them with no load or charging, monitoring the volts for as long as possible. I'd expect a good battery to take several weeks to fall to about 12.5.

Tomorrow you will have taken 24 x 2 = 48 Ah from them ! ........ Only about 25% of their combined total capacity ( Your arithmetic seems dodgy ... or I have misunderstood)

I would then let them stand disconnected for 24 hours and expect them to recover to around 12.4 to 12.5 volts.

Do not run them at 2 amps for more than 48 hours or you will have taken them below 50% state of charge. I would expect a rested ( ie no load for 24 hours ) volts of about 12 .2 when 50% discharged


If you batteries hold their charge they look good for further use.

 

[pcatterall]

Your doing the right thing. Where there is uncertainty, and if time permits, doing a 'discharge test' at around the discharge you may have in practice is a good 'confidence booster' !
As has been suggested just be careful not to discharge below the 50% level. I try to do this test at the start of the season. I find that on resting after a long discharge there is usually a pretty quick 'climb back' to the 'true' resting level.

 

[XDC]

"I would expect a rested ( ie no load for 24 hours ) volts of about 12 .2 when 50% discharged"

Does it matter if a battery drops below 12.2 when actually in use, say running a fridge?

Even from 12.7 mine drop to 12.4 when the 40w fridge is on which gives a very low "range of use" :

12.7 = 12.4 fridge on
12.6 = 12.3
12.5 = 12.2
12.4 resting =12.1 fridge on = > 50% discharged?

 

[Daydream believer]

A domestic battery bank consisting of two 90Ah batteries that are 4 or 5 years old .... correct ?

A month or so ago you charged them , When disconnected they then read 13.3 volts. Fair enough. The reading is good not particularly meaningful .

Today, about a month after they were charged and after standing with no further charge they read 13 volts . That is surprising I would have expected less after a month. Probably no more than 12.8, or thereabouts

A 2 amp load dropped the voltage to 12.77 within seconds.... that's fine. First indications are that your batteries are OK but you need to check that they hold their charge
I would, therefore, have then left them with no load or charging, monitoring the volts for as long as possible. I'd expect a good battery to take several weeks to fall to about 12.5.

Tomorrow you will have taken 24 x 2 = 48 Ah from them ! ........ Only about 25% of their combined total capacity ( Your arithmetic seems dodgy ... or I have misunderstood)

I would then let them stand disconnected for 24 hours and expect them to recover to around 12.4 to 12.5 volts.

Do not run them at 2 amps for more than 48 hours or you will have taken them below 50% state of charge. I would expect a rested ( ie no load for 24 hours ) volts of about 12 .2 when 50% discharged


If you batteries hold their charge they look good for further use.

Vic sorry my arithmetic is wrong. - 2 batteries-i was thinking per battery & forgot to double up for the pair
So after 48 hours you reckon that I should look for 12.2 volts. Anything less & that is the end.??

 

[VicS]

"I would expect a rested ( ie no load for 24 hours ) volts of about 12 .2 when 50% discharged"

Does it matter if a battery drops below 12.2 when actually in use, say running a fridge?

Even from 12.7 mine drop to 12.4 when the 40w fridge is on which gives a very low "range of use" :

12.7 = 12.4 fridge on
12.6 = 12.3
12.5 = 12.2
12.4 resting =12.1 fridge on = > 50% discharged?

I believe that fridges with built in low voltage disconnect (LVD) circuits allow the voltage to fall to about 11.6

Some solar controllers have a power output connection with LVD .... ideal for connecting a fridge

 

[V1701]

"I would expect a rested ( ie no load for 24 hours ) volts of about 12 .2 when 50% discharged"

Does it matter if a battery drops below 12.2 when actually in use, say running a fridge?

Even from 12.7 mine drop to 12.4 when the 40w fridge is on which gives a very low "range of use" :

12.7 = 12.4 fridge on
12.6 = 12.3
12.5 = 12.2
12.4 resting =12.1 fridge on = > 50% discharged?

The batteries will recover to a degree after the load is removed (not immediately though) so although the scenario you've described gives you some clues it does not give a true picture. You'd have to leave the batteries and monitor the voltage drop over time to have a better idea of their state. That said if you're starting off with a rested battery showing 12.4 that is not a fully charged battery...

 

[XDC]

Thanks Vic but is it ok for a battery to sit at say 12.1 whilst the fridge is running?

 

[PaulRainbow]

Thanks Vic but is it ok for a battery to sit at say 12.1 whilst the fridge is running?

Any voltage reading associated with state of charge is a rested reading. 12.1v rested would be lower than i'd want to see my batteries, but with the fridge running a 12.1v reading wouldn't indicate such a low SoC, it would depend as well on how much current the fridge is drawing. I certainly wouldn't want to see 12.1v for long at all.

 

[Daydream believer]

Well I do not have a fridge. But i want to be sure that I can do my ocassional 24 hour SH trips inc night sailing with autopilot working flat out,( if for some reason i am not using the Aeries) my nav lights on & all instruments etc plus intl lights, as & when needed, without having to use the engine half way through the night. I want to know that i am Ok for battery reserve power, if for some reason my starter battery went down, which has been known to happen.
I normally get to a marina within 27 hours & then I am Ok for shore power for 24 hours plus. But I do not want to find that one long trip has suddenly killed the batteries half way through a holiday because they were on the way out. That would mean i would be in trouble on the next long trip without realising & i cannot risk that.
I will have a look tomorrow at 12-00 hours( 24 hour test) & see what it shows. Then if still fairly high I will check again Sunday.(a bit earlier than 12-00) If as Vic says it reads 12.2 then I will stop the test.Hopefully they will not have dropped below 12.2 or at least 12 v. I will allow them to rest for 24 hours & see f they what happens, then stick on charge for 48 hours & see if they hit 13.3 volts again as they usually do.( dropping to 13.0 after 3-4 weeks)

 

[johnalison]

There are many ways leading to Rome, and our cruising needs were similar to yours. We have about 200Ah in three batteries for service, and a 36w solar charger. On the other hand, we have a fridge. I generally expect 5-7 years from basic heavy-duty batteries, but do my best to avoid voltage drops at any time. Batteries can fail quite suddenly, though. Out last lot let us down while in Salcombe and I had to phone someone to deliver them. Without a fridge, I would be inclined to squeeze all I could out of what I had, bit even a small solar panel such as ours can make a useful difference.

 

[Daydream believer]

Just checked after 21.5 hours at 2 amps & they read 11.73 volts. have not checked them after rested but that says to me that considering there should be 180 amp hours of reserve power they are pretty much shot.
Next test is to re charge them. Repeat the test with my starter battery connected & see if it draws anything off the starter battery. I have a new victron VCR fitted last year because my last 35 amp hour red flash starter battery died completely after less than 20 months. I wondered if the domestics were drawing it down.
Presumably, This will tell me if it is properly isolated. The battery charger connects to both batteries but I am not sure that even when not working it could be bye passing somehow via the charger wiring- Is that possible? Presumably it should not & the VCR should disconnect the starter from the domestics at a certain voltage level. Have I got that correct?

 

[PaulRainbow]

Just checked after 21.5 hours at 2 amps & they read 11.73 volts. have not checked them after rested but that says to me that considering there should be 180 amp hours of reserve power they are pretty much shot.

Almost certainly knackered, but leave them for a few hours and check again, just to be sure.

Next test is to re charge them. Repeat the test with my starter battery connected & see if it draws anything off the starter battery. I have a new victron VCR fitted last year because my last 35 amp hour red flash starter battery died completely after less than 20 months. I wondered if the domestics were drawing it down.

You'd need a faulty VSR for that to happen, unlikely, but not impossible. Easy to check though, hook all of the batteries up, but take one red wire off of the VSR, measure between the empty terminal and negative for volts, should be 0, repeat with the other terminal.

Presumably, This will tell me if it is properly isolated. The battery charger connects to both batteries but I am not sure that even when not working it could be bye passing somehow via the charger wiring- Is that possible?

Very unlikely. Easy to check ttough, turn on as much domestic equipment as you can and check the battery voltages, should both be different, if not, there is a fault in the mains charger.

Presumably it should not & the VCR should disconnect the starter from the domestics at a certain voltage level. Have I got that correct?

That's correct.

 

[Richard10002]

Ok here goes for the prize for the one millionth battery thread

Deleted since reading the rest of the thread

 

[BabaYaga]

I have a new victron VCR fitted last year because my last 35 amp hour red flash starter battery died completely after less than 20 months.

Please don't take this wrong, but if you have had a Red Flash starter battery die so soon and now possibly also the AGM house bank after only four or five years, you might want to take a step back and review how your system is set up and managed. To me, this sounds far from normal.
For instance, are you sure that it was a faulty VSR that caused the premature starter battery failure?
I also have a Red Flash starter battery, installed in 2009, still fine. My 240 Ah house bank (wet, leisure type maintenance free) dates from 2011, though probably on its last legs. I run a fridge.

 

[Daydream believer]

I do not know why everyone keeps on about fridges!!!
You are making me feel like a second class citizen
The original unit was a simple voltage relay thingy which I changed last season after a friend felt that there was a problem with it
The new one should be OK but I am a bit paranoid about electric. I can do all the other jobs with ease, but electrictrickery has me stumped.
I have had 2- 3Phase electric shocks in my life & 4 hours in A&E with skin hanging off my burnt hands like curtains & a burn in the top of my head ( cut a wire with a strimmer) does not make me confident. I have hooked a couple with the digger as well

 

[BabaYaga]

You are making me feel like a second class citizen

Sorry, was certainly not my intention. I mentioned fridges as they are known to be a challenge to a modestly sized battery bank.
Perhaps you have just had bad luck with your batteries, but sometimes bad luck is promoted by some deficiency in the installation or handling.
You mention upthread that your battery charger connects to both battery banks. Is it possible that they might have sat for too long at too high voltages?

 

[Daydream believer]

Sorry, was certainly not my intention. I mentioned fridges as they are known to be a challenge to a modestly sized battery bank.
Perhaps you have just had bad luck with your batteries, but sometimes bad luck is promoted by some deficiency in the installation or handling.
You mention upthread that your battery charger connects to both battery banks. Is it possible that they might have sat for too long at too high voltages?

Actually one of the reasons I am also concerned about power is that i am considering a 12/240 coolbox but I did not want to mention that as it would start a massive thread drift. I made a big mistake when I bought the boat by not having the fridge option, but spent the money on a shower instead. I now realise that l it would have been better if I smelled, -----but still had fresh food.
As for the charging I think I am within reasonable limits although even if I have been motoring for several hours the shore power charger still clicks in & shoves in max volts(14.4) dropping to 13.3 over half an hour or so after I arrive. (from memory) Suppliers of Red Flash did say that was Ok.

 

[pvb]

Well I do not have a fridge. But i want to be sure that I can do my ocassional 24 hour SH trips inc night sailing with autopilot working flat out,( if for some reason i am not using the Aeries) my nav lights on & all instruments etc plus intl lights, as & when needed, without having to use the engine half way through the night. I want to know that i am Ok for battery reserve power, if for some reason my starter battery went down, which has been known to happen.
I normally get to a marina within 27 hours & then I am Ok for shore power for 24 hours plus. But I do not want to find that one long trip has suddenly killed the batteries half way through a holiday because they were on the way out. That would mean i would be in trouble on the next long trip without realising & i cannot risk that.

From today's readings, it certainly sounds like your batteries are past their best. However, if you want to do 24 hour trips safely, you really need more battery capacity. Increasing your battery bank to 4 domestic batteries would give you a much better safety margin, and the batteries would last longer too.

By the way, I've found it difficult to get insurance cover for singlehanded trips longer than 18 hours. May I ask who you insure with?