Battery charging - what voltage to stop?

LittleSister

LittleSister

Well-Known Member
Joined
12 Nov 2007
Messages
20,344
Location
Me Norfolk/Suffolk border - Boat Deben & Southwold
Visit site
Due to ill health etc. boat has been out of commission for 18 months. Batteries are off the boat and disconnected, but sadly were left uncharged for last 6 months. I'm now charging them up again (using a distinctly un-smart old car battery charger), and would appreciate advice as to what voltage to stop at - I want the batteries charged as much as appropriate, but don't want to damage them by over-charging. Presumably this can be judged by voltage.

The batteries are -
1) Engine cranking battery - Red Flash 1100, Sealed Lead Acid, about 2 years old.
2) Domestic battery - Lifeline Deep Cycle 105ah, AGM, probably about 5 years old.
3) Spare battery - Varta Blue Dynamic B17 43ah (leisure battery?), age unknown.

After standing for about 6 months the open circuit voltage of the batteries was as follows:
1) Engine Battery - 12.86v
2) Domestic battery - 12.67v
3) Spare battery - 12.5v

After about a week of charging whichever was the lowest each day for a few hours (on 'Normal', not 'Fast Charge' setting), and having stood all today without any charging, the open circuit voltages are now:
1) Engine battery - 13.03v
2) Domestic battery - 12.94v
3) Spare battery - 12.74v

Should I stop now, or continue charging any of them? And once 'fully' charged after how much time, or reduction in voltage, should I ideally charge them again?
 
I'm afraid those open circuit voltages don't mean much as you are only reading the surface charge on the plates. It would be okay if you put say a 10 amp draw on each battery for say half an hour and then take the open circuit reading after the batteries have rested for an hour, but you still wont learn much without a capacity test.

Your AGM and sealed batteries should never be charged with voltage high enough to cause evaporation. This rather depends on the environmental temperature, but the max voltage shouldn't exceed say 14v.

For normal deep-discharge wet lead acids with refill lids, you can charge them up to 15.5V for a couple of hours as an equilization or conditioning charge ..... provided you maintain the electrolyte levels with de-ionised water. This will help break down a sulphate layer on the plates and re-condition the batteries. This will liberate hydrogen so make sure the space is well ventilated.
 
TradewindSailor said:
I'm afraid those open circuit voltages don't mean much as you are only reading the surface charge on the plates. It would be okay if you put say a 10 amp draw on each battery for say half an hour and then take the open circuit reading after the batteries have rested for an hour, but you still wont learn much without a capacity test.
Click to expand...

Do I really need a capacity test to tell how charged a battery is? Just to be clear, I am not trying to find out how much life the batteries have in them.
 
LittleSister said:
Do I really need a capacity test to tell how charged a battery is? Just to be clear, I am not trying to find out how much life the batteries have in them.
Click to expand...

The capacity test is for finding out the health of the batteries. The voltages stated should allow you to charge without damaging your batteries.

As for answering the other part of you question. I would let deep cycle batteries down to about 12.2V whilst in use, but if I was just trying to look after batteries that were not being used I would get a small trickle charger at say rated 2-4% of the amp-hour capacity, i.e 3 amps for a 100 amp hour battery, and just charge it all the time. Without a trickle charger I would recharge when the open-circuit voltage got to 12.5V.
 
LittleSister said:
Due to ill health etc. boat has been out of commission for 18 months. Batteries are off the boat and disconnected, but sadly were left uncharged for last 6 months. I'm now charging them up again (using a distinctly un-smart old car battery charger), and would appreciate advice as to what voltage to stop at - I want the batteries charged as much as appropriate, but don't want to damage them by over-charging. Presumably this can be judged by voltage.

The batteries are -
1) Engine cranking battery - Red Flash 1100, Sealed Lead Acid, about 2 years old.
2) Domestic battery - Lifeline Deep Cycle 105ah, AGM, probably about 5 years old.
3) Spare battery - Varta Blue Dynamic B17 43ah (leisure battery?), age unknown.

After standing for about 6 months the open circuit voltage of the batteries was as follows:
1) Engine Battery - 12.86v
2) Domestic battery - 12.67v
3) Spare battery - 12.5v

After about a week of charging whichever was the lowest each day for a few hours (on 'Normal', not 'Fast Charge' setting), and having stood all today without any charging, the open circuit voltages are now:
1) Engine battery - 13.03v
2) Domestic battery - 12.94v
3) Spare battery - 12.74v

Should I stop now, or continue charging any of them? And once 'fully' charged after how much time, or reduction in voltage, should I ideally charge them again?
Click to expand...
If your batteries were at the voltage you stated after 6 months, I would say they are tickety boo, the 12.86 was fully charged, the others not too bad.
Stu
 
TradewindSailor said:
. . . I would get a small trickle charger at say rated 2-4% of the amp-hour capacity, i.e 3 amps for a 100 amp hour battery, and just charge it all the time. Without a trickle charger I would recharge when the open-circuit voltage got to 12.5V.
Click to expand...

Unfortunately I have no trickle charger. Santa not due for a little while, and hasn't been too forthcoming in recent years anyway!

So, while the batteries remain out of use, I recharge if/when they drop to 12.5v?

But I still don't know the answer to my original question - at what voltage to stop charging! Would this be the 12.86 that Stu mentions as being fully charged?
 
LittleSister said:
Unfortunately I have no trickle charger. Santa not due for a little while, and hasn't been too forthcoming in recent years anyway!

So, while the batteries remain out of use, I recharge if/when they drop to 12.5v?

But I still don't know the answer to my original question - at what voltage to stop charging! Would this be the 12.86 that Stu mentions as being fully charged?
Click to expand...
As I understand it, 12.8v is fully charged, especially as it was stood for 6 months. The voltage you are seeing at the mo is the surface charge left by the charger, I suspect your simple battery charger is chucking 14.6v at them, a good voltage to fully charge batteries BUT not good if you dont keep an eye on the acid levels. I would put a 12v bulb on each separately for a hour to get rid of the surface charge, you should then see 12.8ish, ie fully charged
Stu
 
But I still don't know the answer to my original question - at what voltage to stop charging! Would this be the 12.86 that Stu mentions as being fully charged?
Click to expand...
14.4 would be a sensible voltage at which to charge them ... and the maximum for your Redflash battery. Regard a rested volts of 12.8 ish as the point at which to stop, but see below

The Lifeline ( gosh that was expensive!) can also be given an "equalising" charge at 15.5 volts for 8 hours if it shows signs of capacity loss.

The Varta Blue Dynamic battery is a "SUPERIOR HIGH PERFORMANCE" car battery. It is sealed with plate technology designed to reduce water/electrolyte consumption to a minimum. A very low self discharge rate is claimed making storage for up to 18 months possible.
For all that a relatively inexpensive battery!

Regarding the rested volts ( ie after 12 hours with no charge or discharge). There is a considerable variation in the voltage you may find for a fully charged battery illustrated below.

For maintenance purposes an inexpensive multi-stage charger like those offered periodically by Aldi and Lidl might be worth having. http://www.aldi.co.uk/uk/html/offers/special_buys3_15825.htm?WT.mc_id=2010-10-04-14-05
or for more ££s one from Ctek http://www.ctekchargers.co.uk/productindex.php

wp834ca5fb.png
 
It's not only the maximum voltage, it's also how long and at what current.

Vic's right about the 14.+ V, and if you've only got that automobile charger you shouldn't be able to do them any harm.

The voltages sound good for batteries left that long. They should be able to be reused for awhile at least.

While UK skippers tend and Sterlings tend to charge batteries at higher voltages than we do here in the US, a good "How To" about batteries can be found in the Ample Power Primer, use the tech tab to download it, from www.amplepower.com

Some of the answers you're looking for and some you may not have thought to ask are in there. Regardless, it's good reading and a good learn.

Good luck with batteries, glad you're back to the boat. I broke my leg skiing in early 2009, so I understand the withdrawal feelings.

It also sounds like you've finished charging, the second round of voltages after resting looks pretty good.
 
Last edited:
Battery charging

I tend to agree with Tradewind Sailor it is current and time that charge a battery. If you charge at lower current then you can not really harm the battery by overcharge. Larger currents should be restricted to something like the Amp hour capacity of the battery.
Using voltage as a means of determining when to stop charging and indeed the % charge of the battery is not a very good way to go. However we use it because it is so easy to measure. Or so easy to use a pointer to charge state for auto charging. olewill
 
Or 24 hours might be better.
Click to expand...
I would not disagree with that but impatience usually gets the better of me. I charge a battery one day. Leave it stand over night and check it mid morning the next day.
 
You need to know what voltage your battery charger achieves before you can answer your question. If it only charges at 12.8v on "normal" (which would be trickle on an old charger) then you will never get battery voltage above that. 13.8v is a good indication of full charge. When you can afford it get one of these, Numax Marine Battery Charger 12V 10A. They are cheaper than the equivalent supposed "top notch" Ctek chargers but do what the're meant to do, look after your expensive batteries, just as same. No, I don't have any connection with them (pardon the pun) but I am an electrician and research as much as I can. I take my batteries off the boat over the winter and leave them connected to the charger till spring.
 
Having just put a new battery into the boat, I was curious to see whether the battery was at 100% or not and recalled an article in Good Old Boat for a simple way of checking the state of your batteries. The article suggested a rough method was to use a multi meter and check the voltage. The article had a table from a couple of battery manufacturers, and checking up the manual for the Trojan Battery Company, sure enough they suggest that a flooded lead acid battery with a voltage of 12.73 is 100% charged. You can find the table in the manual here if you're curious (gives specific gravity values too).

http://www.trojanbattery.com/pdf/UsersGuide_English.pdf

FWIW, The Good Old Boat article also had a table for Gel & AGM too all of which say that 100% is 12.8+.


Not sure of it's relevancy to your situation, but does seem to match what others are saying here. I've now printed the table off, and am going to paste it in my battery compartment for when I am curious about the state of it (she's only a little boat, so am not going to spend too much money on battery monitors etc...).

Cheers, PT.
 
I think that a very good investment is a battery charger that goes onto a floating maintainance charge after battery charging is complete. I bought mine in Argos ages ago and it wasn't very expensive at all. It just takes away the guesswork and means that if you forget to disconnect it won't do any harm, and if you wish you can just leave it connected, though I don't.

Mines a "Challenge" fully automatic..11 Amp. It has a setting for ordinary lead acid where it charges at 15.3v and a setting for Gel/Sealed etc. at 14.3v. It has a 'bike' setting for batteries of 5-20Ah and a car setting for batteries of 27-110Ah. Once charging is complete (green LED) it goes onto 13.6 float charge.

I'm so besotted with it I even gave my old charger away...:D:D

Tim
 
Last edited:
Alfie168 said:
Mines a "Challenge" fully automatic..11 Amp. It has a setting for ordinary lead acid where it charges at 15.3v and a setting for Gel/Sealed etc. at 14.3v. It has a 'bike' setting for batteries of 5-20Ah and a car setting for batteries of 27-110Ah. Once charging is complete (green LED) it goes onto 13.6 float charge.
Click to expand...

I do have a 'spare' far from new but modern-ish looking Halfords charger which though not 'smart' has different settings for 'maintenance free' and 'normal' batteries, a series of LED lights to indicate how charged one's battery is, and which switches off automatically when full charge is reached. However, I avoid using this as it as it always shows all my batteries, even ones that I know work fine in use, as not holding a charge, and never seems to fully charge them, voltage wise.

Instead I use an even more ancient (1970's?) cheap looking 'ABSAAR' charger which even has a 6 volt setting (I think it's a while since anyone made 6 volt cars or bikes!). I've was just trying to check the voltage. Open circuit on 'normal' charge it showed only 12.1 volts, and 'fast' charge something like 13v, but it obviously does more than that in use. Having had it on my spare battery, which was previously reading 12.7v, for about 10 minutes it's settled down to 15.08v on 'normal charge, and rises to 15.45v if i switch it to 'fast. Sounds a bit high, doesn't it?

Of course, I've no idea how accurate my (Draper) multimeter is! My other multi-meter (also Draper, but different model) reads about 0.7v higher, but I don't trust this one as since its new internal battery it doesn't return to zero, and always reads minus a volt or so when unconnected to anything.

You're right, a modern 'smart' charger would be one answer to my current (geddit?) situation of trying to keep the batteries charged while the boat's out of commission, but normally the boat's in use and they're kept charged by the boats engine with no problems.
 
VicS said:
The Lifeline ( gosh that was expensive!) . . .

The Varta Blue Dynamic battery is. . . For all that a relatively inexpensive battery!
Click to expand...

The Lifeline wasn't too expesnive, Vic, as it came with the boat (which was!). It is, though, enormously heavy. Far too heavy for our little boat, really, and we'll get something lighter when it gives up the ghost. It's also very big. It's only because it can live on it's side it fits in any of our lockers at all!

The Varta was indeed cheap. I think I paid a tenner for it second-hand at a boat jumble some years ago. It's intended role was to provide some electrickery for nav lights on our previous even smaller boat with no charging facilities, and the battery was to be charged at home and carried backwards and forwards (it even has a handle!). I never got round to wiring the boat, and kept the battery when we sold it. The Varta was later pressed into service as an engine battery for our current boat when the Red Flash that came with it suffered a cell short-out. The Varta did the job fine, but was too big to fit in the locker with the Lifeline, so spent about a year getting in the way on the quarter berth, held firmly in place by a web of gaffa tape. (We have the technology!) When we couldn't stand it getting in the way any more, we splashed out and bought a replacement Red Flash (ouch!) to fit in the size-specific compartment that had been installed in the boat. (The Red Flash batteries are amazingly small for the big currents they knock out for engine starting.)
 
You must log in or register to reply here.

Share this page

Top