Lead Acid Batteries - leaving them partially discharged?

[Tim Good]

House Bank: 4 x Trojan T-105 (2018)
Solar: 360w

Short version:

How long can I leave my batteries discharged (no lower than 50%) without causing lasting damage).

Long version:

I know this topic is done to death, but I suppose I wanted the pragmatic view rather than best practice.

We all know wet lead batteries like to be fully charged. I’ve met people that don’t like to leave them more than 24 hrs without ensuring a full charge again.

I think I’m somewhere in the middle but I don’t feel I’m making full use of the batteries and they’re probably going to outlive me or the boat before they’re used properly.

I always try and ensure they get a full charge to float every few days and top them up / measure the SG every 1/4.

I’m think I’m being too precious about them and I should use them more. We do charge out electric outboard, boiler water electrically etc but I tend to avoid doing such things if they haven’t gone to full charge again in a few days.

What’s general consensus?

 

[Bobc]

T105s are very tough batteries. They are one of the few that will bounce back after being discharged for a while. So long as you keep them above 12v, they should be fine left for months.

 

[vyv_cox]

During lockdown my batteries were left disconnected for just over three years. By the time we returned to Greece their voltage was down to 12.4V. They started the engine and appear to have recovered completely.

3 x Winner Solar 110Ah, two years old before covid.

 

[geem]

It depends how long you expect them to last. Charging them to float every day should ensure they last. The only way to know what condition they are in at the moment is to charge them up fully and put a tester on them

 

[MontyMariner]

With 360W of Solar they will recharge in your absence, I don't see an issue.

 

[Tim Good]

With 360W of Solar they will recharge in your absence, I don't see an issue.

We’re liveaboards. I’m talking about ongoing use rather than using and then leaving the boat.

So for example I’m wondering if using the batteries down to 50% regularly and only bringing them back to float once a week or every 2 weeks is ok.

 

[MontyMariner]

We’re liveaboards. I’m talking about ongoing use rather than using and then leaving the boat.

Ah! Got you.
How long a period does it take for them to discharge from float to 50%?

 

[Tim Good]

Ah! Got you.
How long a period does it take for them to discharge from float to 50%?

Good question. Quite a while since the solar keeps adding. During sunny times almost never. But for example this week ahead then it might take 4/5 days since forecast is rubbish.

But depends if we decide to keep hammering them with the inverter and using kettle etc.

 

[Neeves]

Out of interest - how do you monitor the battery state. Your quantitative data is based on '50%' ? and you measure SG. Where does your 50% come from? My guess is that your 360W of solar is not enough and the solar contribution will reduce as winter draws in - which means you will increasingly need to recharge -another way (which is what yo are saying on post 8) - or invest in more solar and find another way to make a cup of tea.

I understand why you asked the question.

Jonathan

 

[RunAgroundHard]

I have 4 x T105s for domestic and old Lucas alternators, also a Sterling Pro Charge Ultra. My sailing style is weekend jaunts, occasionally a week away from time to time, all year use of boat. I sail a lot, so engine is really used for berthing manoeuvres until sail are hoisted. Demand is fridge, Raymarine 12" plotter, pressurised water pump, LED lights (navigation and illumination); so not heavy use.

When I get back, I plug in to mains and charger kicks in. Sometimes I stay overnight on return to marina and charger stays on, sometimes I clean the boat and leave about 3 to 4 hours later. I always switch off the mains power and disconnect shore power when I leave boat. It is just a thing I do. I work away from home on overseas projects, so the boat can be left easily for 4 to 5 weeks unplugged.

So far with this type of use, with 7 year old T0105s, they are still good. They get up to float easily and stay charged for along time. When I return they do not take long to get back to float. I would suggest that your use is not problematic for the batteries.

 

[Tim Good]

Well ud

Out of interest - how do you monitor the battery state. Your quantitative data is based on '50%' ? and you measure SG. Where does your 50% come from? My guess is that your 360W of solar is not enough and the solar contribution will reduce as winter draws in - which means you will increasingly need to recharge -another way (which is what yo are saying on post 8) - or invest in more solar and find another way to make a cup of tea.

I understand why you asked the question.

Jonatha

Out of interest - how do you monitor the battery state. Your quantitative data is based on '50%' ? and you measure SG. Where does your 50% come from? My guess is that your 360W of solar is not enough and the solar contribution will reduce as winter draws in - which means you will increasingly need to recharge -another way (which is what yo are saying on post 8) - or invest in more solar and find another way to make a cup of tea.

I understand why you asked the question.

Jonathan

During summer the 360w keeps well up and yielding 2kwh a day is common.

My question really stems from the fact we’ll eventually go to lithium and we plan on 600w of solar in the coming years. So really it’s a case of will I be ok to hammer them more. We ideally like to cook on induction also but that’s only really possible in May, June and July when we seem to make more than we can use.

It just seems pointless have 900ah of capacity and using 25% of it. Seems crazy.

 

[noelex]

Ideally, lead acid batteries prefer to be charged to 100% after every cycle, but doing this every few days will make little practical difference in the lifespan of flooded lead acid batteries. You could afford to extend the time when the battery is at PSOC (partial state of charge) considerably and still have a reasonable life span.

The most important factor is to ensure the battery voltage set points are suitable so the battery is reaching 100% SOC occasionally, and to keep the depth of discharge as low as possible. Batteries are made to be used. Don’t fret about minor departures from the ideal that will only result in a small change from the longest battery life.

 

[Neeves]

It just seems pointless have 900ah of capacity and using 25% of it. Seems crazy.

You need to cater for the days when there is little sun, or the sun cannot shine on the panels (you are sailing in bad weather) which means having excess battery and solar capacity.

My understanding from reading the threads here is that whatever is the ideal practice for lead batteries need be ignored if you plan to move to lithium (but maybe this is years away - unless you are going to chuck good lead batteries). You could do what Geem is doing, I think, and he runs both Lithium and Lead as independent systems.

It may seem crazy to use only 25% of capacity but it is equally crazy to ignore the inefficiencies of, say, your fridge. Equally using a panel whose output has not been checked against its spec seems equally crazy - but some don't think this necessary.

Jonathan

 

[B27]

House Bank: 4 x Trojan T-105 (2018)
Solar: 360w

Short version:

How long can I leave my batteries discharged (no lower than 50%) without causing lasting damage).

Long version:

I know this topic is done to death, but I suppose I wanted the pragmatic view rather than best practice.

We all know wet lead batteries like to be fully charged. I’ve met people that don’t like to leave them more than 24 hrs without ensuring a full charge again.

I think I’m somewhere in the middle but I don’t feel I’m making full use of the batteries and they’re probably going to outlive me or the boat before they’re used properly.

I always try and ensure they get a full charge to float every few days and top them up / measure the SG every 1/4.

I’m think I’m being too precious about them and I should use them more. We do charge out electric outboard, boiler water electrically etc but I tend to avoid doing such things if they haven’t gone to full charge again in a few days.

What’s general consensus?

The way I see it, batteries have a limited life, they die of calendar months however well you treat them, and everything you do is only accelerating that process to a greater or lesser degree.

So every time you use the battery, that has a cost. IF you flatten the battery to 10% SOC that has a bigger cost than taking it to 50%. Every day you leave it partially charged, that has a cost, assuming it's lead-acid.
Some of these costs are worthwhile, there is a benefit to having the fridge running, or using the heater, or the nav lights to go sailing.

If you live aboard, 200 days a year, you might be looking at 1,000 daily cycles being the life of a battery. So you'll need to keep discharge to no lower than 50% to make that happen.
A 'leisure sailor' might only get 100 nights aboard in a 5 year battery life, so there is less point in worrying about some of those cycles being a bit deeper, or some of the re-charges being a bit slow or delayed.

OTOH, if my battery was low right now, I'd be thinking there's little prospect of the solar recharging it in the next few days, so I might as well run the engine a bit more and give the battery a chance.


for my boat, it's all very small scale, I currently have a single battery as my house bank, a new one is about £90 so if I treat it really nicely and get 8 years from it instead of 4, I'm not saving much.


The other interesting question, is how do different people decide battery has reached the end of its life?

I guess if you have a reasonable battery monitor, you will observe the capacity decreasing over time, and that process will eventually start to accelerate?
At the moment, I'm really not sure how much capacity my battery has lost from new. And I don't have a fixed number for the minimum I could live with.

 

[alahol2]

for my boat, it's all very small scale, I currently have a single battery as my house bank, a new one is about £90 so if I treat it really nicely and get 8 years from it instead of 4, I'm not saving much.


The other interesting question, is how do different people decide battery has reached the end of its life?

I guess if you have a reasonable battery monitor, you will observe the capacity decreasing over time, and that process will eventually start to accelerate?
At the moment, I'm really not sure how much capacity my battery has lost from new. And I don't have a fixed number for the minimum I could live with.

When I start to wonder about my house battery (single 110Ah sealed LA), usually after 4 or 5 years, I do a capacity test. Disconnect the battery, attach a largish known load eg a couple of headlamp bulbs and note the battery voltage and current draw with multimeters every half hour or so. Taking it down to a terminal voltage of about 11.5v then graphing the results can give a fairly good indication of the current capacity of the battery. The last one I ditched was down to about 50Ah after 6 seasons' use. The previous one did 7 seasons to about the same capacity.

 

[B27]

When I start to wonder about my house battery (single 110Ah sealed LA), usually after 4 or 5 years, I do a capacity test. Disconnect the battery, attach a largish known load eg a couple of headlamp bulbs and note the battery voltage and current draw with multimeters every half hour or so. Taking it down to a terminal voltage of about 11.5v then graphing the results can give a fairly good indication of the current capacity of the battery. The last one I ditched was down to about 50Ah after 6 seasons' use. The previous one did 7 seasons to about the same capacity.

The problem is, to properly do a capacity test that way requires starting with a fully charged battery, for which you need some hours of charging. Then you need to re-charge afterwards, which will need ample power for 12 hours or more.
My solar panels are not going to deliver that in the next week or so.

AIUI, most modern cars are using much quicker techniques to measure battery parameters continuously.

I think it's also the case that 'start/stop' batteries spend much of their time partially discharged when the car is parked up, yet they tend to give good service for several years.

 

[Poey50]

When I start to wonder about my house battery (single 110Ah sealed LA), usually after 4 or 5 years, I do a capacity test. Disconnect the battery, attach a largish known load eg a couple of headlamp bulbs and note the battery voltage and current draw with multimeters every half hour or so. Taking it down to a terminal voltage of about 11.5v then graphing the results can give a fairly good indication of the current capacity of the battery. The last one I ditched was down to about 50Ah after 6 seasons' use. The previous one did 7 seasons to about the same capacity.

Excellent idea but even better with a constant current capacity tester. Just leave it to do it's job and read off the figures when it has done its business. Charge back up to completely full (not just to float) immediately to avoid damage. Ridiculously cheap from AliExpress.

https://www.aliexpress.com/item/100...8ae617d493e8983ebb685cdd3ab&afSmartRedirect=y

To improve the accuracy of battery monitors you can do it once per year and then dial in the new (reduced) capacity to the monitor.

It does need the availability of a mains charger as B27 mentions.

 

[alahol2]

The problem is, to properly do a capacity test that way requires starting with a fully charged battery, for which you need some hours of charging. Then you need to re-charge afterwards, which will need ample power for 12 hours or more.
My solar panels are not going to deliver that in the next week or so.

AIUI, most modern cars are using much quicker techniques to measure battery parameters continuously.

I think it's also the case that 'start/stop' batteries spend much of their time partially discharged when the car is parked up, yet they tend to give good service for several years.

Yes, I do this test when the boat is ashore for winter and I have a power source.
Funnily enough my current house battery is an EFB start/stop battery. The characteristics sounded as though they may match marine use better than the usual 'leisure' battery.

 

[B27]

Yes, I do this test when the boat is ashore for winter and I have a power source.
Funnily enough my current house battery is an EFB start/stop battery. The characteristics sounded as though they may match marine use better than the usual 'leisure' battery.

The battery in my boat is a Hankook, it's the popular 110Ah leisure battery size, It's labelled 'dual purpose' but is a lead/calcium battery, in common with many stop/start units.
This does seem to mean the voltages for a given state of charge are 'a little higher', so it's hard to know its exact status.
The receipt is in the file from the previous owner somewhere, it seems to have survived several years of abuse and neglect.

 

[alahol2]

The battery in my boat is a Hankook, it's the popular 110Ah leisure battery size, It's labelled 'dual purpose' but is a lead/calcium battery, in common with many stop/start units.
This does seem to mean the voltages for a given state of charge are 'a little higher', so it's hard to know its exact status.
The receipt is in the file from the previous owner somewhere, it seems to have survived several years of abuse and neglect.

My battery is a Yuasa M31 EFB from Tayna. Fitted last year at which time it was about 30% cheaper (around £105).
It seems to be working fine but with only near 2 seasons use time will tell. I have a 30W solar panel and cheap controller which usually manages to get the battery back to '100%' charge during the week. Alternator gets maybe an hour per trip.
Previous batteries have been similar to yours (dual prpose lead/Ca 110Ah) and lasted 6/7 years before capacity became too degraded.