Maintenance Free Batteries

[Caroline Joan]

I have 2 x 175ah Bosch deep cycle maintenance free house batteries that are 2 years old.

I have always left them charging using my 420watts of solar panels for the 6 months I am not in europe but back home in NZ. Also have 75ah Bosch Starting battery.

How do I check that the batteries are still in good condition as they are sealed?

Also how many Amp Hours are my 3 solar panels (3x140w mono) capable of charging?
Is it right to say 420w divided by 12v = 35amps per hour.
If there is 10hrs on average of daylight then Panels will give 10x35=350ah, which is what my 2x175ah batteries total.
There is probaly some sort I loss I have to take into account plus I have a 75ah starting battery but that is only use 1-2 times a week on average as I tend to anchor for several days at a time.

If I find my batteries need replacing is there any point in buying a size greater than 2x175ah? Or is this too much for 420w solar panels to fully maintain the charge?

I do have a smart charging system for Solar & shore power (hardly on shore) that stops overcharging, handles floating etc - can't remember brand as I'm here in NZ. Will be back in Leros next week!

Any help greatly appreciated.

[Mike OReilly]

There are far more knowledgable folks on here who will likely jump in, but I’m interested b/c I too have sealed, i.e. “maintenance free” wet cell batteries. I wish I didn’t, but that’s another story…

The two ways I know of for testing the health of these batteries are to use a load tester device, or to test resting voltage. In the latter case the batteries need to be isolated, and have been completely at rest (no charging or discharging) for something like 12 hours — the longer the better.

Each battery will be slightly different, but here’s a table of from Trojan on what your resting voltage means:

100% = 12.73
90% = 12.62
80% = 12.50
70% = 12.37
60% = 12.24
50% = 12.10
40% = 11.96
30% = 11.81
20% = 11.66
10% = 11.51

As to how big a bank your solar system can maintain, the answer depends in part on the kinds of loads you put to the batteries. IOW, how deeply do they typically get drained?

I believe your calculations are correct, but that only gives you a theoretical maximum output. That’s useful, but your usage pattern will also have to be considered.

I think your solar is more than adequate to manage a 350 amp-hr bank, but like I say, it depends on your discharge rate. In my case I have a 320 amp-hr bank, and my 400 watt solar system is easily able to fully charge the bank most days.

[Caroline Joan]

Hi Thanks. When it comes to usage, All my lights are LED & I run an electric fridge - can't remember watts but it was fairly low.
I use Autopilot and chart plotter & VHF at sea. Occasionally Radar. I don't have heaps of greedy gear.
Even so 2-3 times a month the battery alarm goes off in the early morning (while still dark) and the meter will read around 11.2 from memory.
It always surprises me as once at anchor I'm really only using LED cabin lights & maybe 1 hour of radio (Music). The fridge is all serviced & operating efficiently - well gased up, theromsat all ok and not too lowly set.


So over the last 2 years the alarm has probably gone off 30-40 times. When the sun sets and not longer charging, I recall Meter reading over 13volts. So a low battery alarm in the morning surprises me. I must be missing something?

[sailorboy1]

Resting voltage will tell you they charged. But only a load test will tell you if the batteries have life still.

420w should easily be able to charge 350ah of batteries if they aren’t being used much (my 390w keeps the batteries charged with frig on as long as I’m away and not using other power)

[smac999]

battery voltage should not be going below 12v. if you low voltage alarm (11v?) has gone off 30-40 times you are hurting those batteries badly.

the best test is to do a 20 hour c20 discharge test. you can google it.

if you replace them. do not get sealed flooded batteries.

[Mike OReilly]

Caroline, my understanding of voltage measure is the 11.2 is dead … beyond dead really. You can drain batteries, especially deep cycle wet cells, to dead. But it will have an impact. And the more often you do it, the worse they get. If you’re bank is measuring that low on a regular basis, I bet it’s dead.

Caroline, you have to measure your draws using an amp meter (ideally battery monitor). A secondary method will be to calculate the draws based on each load x time used. It’s really impossible to say what your load is just from your list.

Don, my understanding (from my reading, and from gurus like MainSail), is that resting voltage is a reasonable measure of battery capacity. The batteries have to fully charged, then left for at least 12 hours. More is better. The resting voltage after this time will give a general measure of the capacity remaining in the battery … unless I’ve completely misunderstood all the resources that are available online and elsewhere, including Mainsail.

[arsenelupiga]

sealed maintenance free batteries are excellent. dont understand why people bash them. I have them now EXIDE 5 years and still hold above 12.5V with fridge running just before sunrise.

However I have 360 W of solar and 480 AH of batteries and typically spend from unset to sunrise overnight 30-40 AH.

So maybe your installation is inadequate.

[StuM]

Originally Posted by Caroline Joan

Also how many Amp Hours are my 3 solar panels (3x140w mono) capable of charging?
Is it right to say 420w divided by 12v = 35amps per hour.

No. But it is right to say 420W divided by 12V = 35 Amps ("without the per hour")

If there is 10hrs on average of daylight then Panels will give 10x35=350ah,
which is what my 2x175ah batteries total.

For most of those hours the sun will not be perdepdncular to the panels and you will get nowhere near 35 Amps from them (in fact, you will probably never see 35 Amps from them since they thhos 420 Watts need to be at a lot more than 12V to charge your batteries. You are more likely to be getting 30 Amps at midday charging at around 13.5V.

The rule of thumb is to work on 4 - 5 hours "full sun equivalent" per day, so you are looking at around 1900Watt hours (Wh) and 150 Amp hours per day.

If I find my batteries need replacing is there any point in buying a size greater than 2x175ah? Or is this too much for 420w solar panels to fully maintain the charge?

It all depends on how much power you use. Calculate how many Ah you use overnight. Double that and that's the minimum battery bank you need. (That assumes that you can get the bank fully charged by late afternoon.).

[btrayfors]

Originally Posted by Mike OReilly

Caroline, my understanding of voltage measure is the 11.2 is dead … beyond dead really. You can drain batteries, especially deep cycle wet cells, to dead. But it will have an impact. And the more often you do it, the worse they get. If you’re bank is measuring that low on a regular basis, I bet it’s dead.

Caroline, you have to measure your draws using an amp meter (ideally battery monitor). A secondary method will be to calculate the draws based on each load x time used. It’s really impossible to say what your load is just from your list.

Don, my understanding (from my reading, and from gurus like MainSail), is that resting voltage is a reasonable measure of battery capacity. The batteries have to fully charged, then left for at least 12 hours. More is better. The resting voltage after this time will give a general measure of the capacity remaining in the battery … unless I’ve completely misunderstood all the resources that are available online and elsewhere, including Mainsail.

No, Mike. Resting voltage can indicate how fully charged the battery is (state-of-charge), but it does NOT give you an indication of battery CAPACITY. These are totally different things.

Resting voltage gives you an indication of state-of-charge (SOC), i.e., how fully charged your battery is.

Battery capacity, by contrast, can only be accurately measured thru use of a controlled 20-hour discharge protocol. It can be less accurately estimated thru a number of "battery testers", including the very expensive models which measure inductance. These are less than totally accurate; I'd call them "indicative", and only if you know what you're doing.

Consider this: it's perfectly possible to have a fully-charged battery which has over the years lost 50% of its capacity, and which shows 12.6VDC resting voltage, but which in reality can only deliver 50% of its rated capacity.

Pracically all of us have actual experience with partial-capacity: our automobiles and trucks. Even though partially compromised, these batteries will start the vehicle nicely every time, up until the time they won't.

Truth is, they've been losing capacity daily ever since installation. We just don't notice it until the engine won't start.

Bill

[sailorboy1]

Originally Posted by Mike OReilly

Don, my understanding (from my reading, and from gurus like MainSail), is that resting voltage is a reasonable measure of battery capacity.

You need to read it again. As an example recently my starting battery had great resting voltage, but didn't have enough capacity to start anything.

[john61ct]

Originally Posted by arsenelupiga

sealed maintenance free batteries are excellent.

They are more expensive, require more stringently regulated charge sources (expensive), don't allow specific gravity testing and don't last as long.

Some people feel not having to water outweighs all that.

Their real USP is the ability to install sideways when space is limited. The high CAR aspect is not all that helpful when the goal is to get to true 100% Full.

[robert sailor]

Originally Posted by Caroline Joan

Hi Thanks. When it comes to usage, All my lights are LED & I run an electric fridge - can't remember watts but it was fairly low.
I use Autopilot and chart plotter & VHF at sea. Occasionally Radar. I don't have heaps of greedy gear.
Even so 2-3 times a month the battery alarm goes off in the early morning (while still dark) and the meter will read around 11.2 from memory.
It always surprises me as once at anchor I'm really only using LED cabin lights & maybe 1 hour of radio (Music). The fridge is all serviced & operating efficiently - well gased up, theromsat all ok and not too lowly set.


So over the last 2 years the alarm has probably gone off 30-40 times. When the sun sets and not longer charging, I recall Meter reading over 13volts. So a low battery alarm in the morning surprises me. I must be missing something?

Hi there...If you allowed your batteries to get to 11.2 volts 30 or 40 times you will have effectively reduced the longevity of your batteries by a lot. I expect that the plates will have sulphated because of your deep discharges and rarely getting fully charged again.
Depending on your battery type you may be able to equalize them to help restore some of the lost life but check with the manufacturer before doing this.

[Mike OReilly]

Originally Posted by btrayfors

No, Mike. Resting voltage can indicate how fully charged the battery is (state-of-charge), but it does NOT give you an indication of battery CAPACITY. These are totally different things.

Thanks Bill/Don, I love learning what I don’t even know I don’t know .

So… a resting voltage measure give no information about remaining battery capacity? Will a typical wet battery continue to show 12.7 resting voltage once it has hit, say 50% capacity? I’m pretty sure my last set of batteries did show a reduced resting voltage at the end of their life.

Bill, can you recommend a battery tester that is worth the money? I can’t afford the best, but now you’ve got me wanting to get something.

[sailorboy1]

[QUOTE=Mike OReilly;2588585 Will a typical wet battery continue to show 12.7 resting voltage once it has hit, say 50% capacity? [/QUOTE]

My last start battery had 12.7V resting with 2 plates uncovered and stuff floating in the cells. It wouldn't ever turn my generator and the voltage would drop so low when trying that the panel would shut off. I'm sure it was much less than 50% capacity.

[john61ct]

State of Charge, SoC means how much energy is currently stored in the bank, usually as a %age.

So if capacity when new is 400AH, in those first few months after breaking in, the guideline is don't remove more than 200AH except for rare necessary circumstances.

Going much lower regularly shortens bank life. So does not getting back to true 100% Full regularly.

Which means accelerates the inevitable decline in capacity, or State of Health.

After a couple years of coddling, SoH may be 90%. That means the bank only holds 360AH, and that 50% cutoff is now 180AH not 200.

After five years it may be 75%, and industry standard would be to scrap the bank and replace it, long before an "unexpected sudden failure" would occur.

Many people staying close to home don't worry and use the bank until it fails. Cruisers living on the hook in third world regions should be more informed and cautiously proactive.

Those using coulomb-counting SoC meters need to keep them programmed with the residual capacity as it declines over time.

There is no gadget that will tell you SoH accurately. You need to have a proper 20-hour load test run, Maine Sail's HowTo site gives a step by step for that.