12 V starter battery

I have a 12V battery, not used on a car but is connected to a 12V recovery winch in a boat shed.
This is kept between use connected to a CETEK MXS 5 - an 8 step charger with correct Float charge once up to full charge.

Over winter I remove and put indoors, and leave it on the charger.
The same charger wired in parallel across a pair of batteries (worked fine on previous years)
Fitted it on w/end and it was dead ..... So to be sure put it on the charger again for 24 Hrs
Now it appears to be working fine.

Checking voltage ..... it measures 13.5V after charge - which I can only think must be a surface charge. (i.e greater than ~12.6)
I used the winch to pull in a 2.5T load, and seemed OK, Voltage after the recovery was 12.75V

Would this suggest battery is probably OK ?

Perhaps having the charger across 2 batteries, when one of them was new and higher capacity, may have provided imbalance and it shut down charging due to back emf of the larger battery and then failed to charge the winch battery ?

Next year I'll use separate chargers.

You can buy yourself from Aldi or Lidl a smart charger for around £13 which is a rebranded ctrl

For cheaper than killing a battery because you're not keeping it charged

Did you mean rebranded CETEK ?
That would be next Oct, as kits now connected to CTEK charger for next 7 months.

The battery is fine. You can buy simple load meters which will tell you whether it needs replacing or not.

Keep in mind that even batteries with regular topped up charging still dont last forever.

Generally a battery will have a life expectancy of around 5 years, any more than this and you've had a result. Even the new fandango gel batteries still only have a life expectancy of 5 years

Well it’s 9 yr old now.
But does not get daily use ... and not taken to full discharge.
Importantly not connected to an engine so Max charging rate is 5A

I am aware of drop testers, but not load meters.
The usual issue is voltage down as a cell has gone short circuit ...but it’s well over 12V hence my question.

RickH said:

Checking voltage ..... it measures 13.5V after charge - which I can only think must be a surface charge. (i.e greater than ~12.6)
I used the winch to pull in a 2.5T load, and seemed OK, Voltage after the recovery was 12.75V

Would this suggest battery is probably OK ?

Click to expand...

Yes, my advice is not to keep a battery on permanent charge, rather to bring them to a full charge periodically if they have not been used. They constant charge, even on an intelligent charger, can cause the electrolyte to evaporate. I've wrecked several batteries in the past doing that, especially caravan batteries which can be stood for months unused. My regime now is one of bring them up to full charge once a month, once every two months, then give a full charge over around two days when I plan to use the caravan.

I do similar with my car, whilst it is parked unused for weeks on end - a 20 minute charge, just once per day, then off the rest of the time. My caravan's battery must be around 10 years old by now, it is only there to supply caravan mover power. I recently bought a clever battery diagnostic unit, having so many batteries around the place - testing the caravan battery, it shows it as 93% good.

RickH said:

The usual issue is voltage down as a cell has gone short circuit ...but it’s well over 12V hence my question.

Click to expand...

At 12.75v you don't have a dead or dying cell, but voltage alone is not the end of the story - the cells could all be down on actual capacity. This latter is why they use a discharge tester - basically apply a load and see what happens to the voltage under load.

I have a few sealed Lead Acid batteries some of which are 8 years old and still have more than 80% ( estimated ) of their rated capacity.

They are kept on float charge at 13.8 Volts ready for when ever they are needed. Most frequent use is for temporary event lighting.

Understand your approach. That is exactly what the CETEK does ... charges through stages as required, then puts it on a fully controlled float charge.

Harry Bloomfield said:

Yes, my advice is not to keep a battery on permanent charge

Click to expand...

I would agree on a trickle charger, it simmers the battery - but a correct float charge is designed specifically for permanent connection.
https://homebatterybank.com/trickle-chargers-vs-float-chargers/

RickH said:

I would agree on a trickle charger, it simmers the battery - but a correct float charge is designed specifically for permanent connection.
https://homebatterybank.com/trickle-chargers-vs-float-chargers/

Click to expand...

Any current passing through a battery, even a float charge will evaporate the electrolyte. I have had float chargers wreck batteries in the past, so experience teaches me not to do it. Float is fine, if you expect to imminently need the power of the battery ready to use, if not, then no need for the float charge. However, batteries do self discharge, so a regular routine is needed to bring them back up. My batteries can happily sit for months, between my running a maintenance charge session - when not connected to anything.

My car's battery is rather different, in that on the car it discharges at 20mA, which if left with no charge could flatten it over a month or so - as is common with all modern cars packed with electronics. That gets a 20 minute boost, each day, to replace the discharge, whilst ever my car is parked up.

The Lidi, Ctek and other smart chargers are not all the same, each has a slightly different way to get same result, I have found temperature does affect batteries, and also it can take a long time to fully recharge a lead acid battery.

But the Lidi has 5 charge rates, two once completed it will not auto return, so leaving the battery on charge for an extended time it will charge at 0.8 amp, 0.1 amp or zero. And even a 40 AH battery at 0.1 amp in good condition will hit 14.4 volt and switch off, so left connected to the battery charger does not mean it is being charged, the battery voltage will slowly decay, and once it dips below 12.8 volt the charger will switch back on, or increase charge rate in the main for just a few minutes then it will switch down or off again.

I do see there is a small problem, with the cheap Lidi charger there is no time out, more expensive types do have a time out, so a battery with a shorted cell can charge at 3.8 amp for weeks, also if the battery self drain is just under 0.1 amp it can sit above 13.4 volt (standard float charge voltage) for an extended time, however just a glance shows the battery voltage, and if it is sitting at between 13.4 and 14.4 volts for an extended time, then it does need switching off manually.

However I use the Lidi charger on 6 batteries at 12 to 95 Ah, and many smaller batteries, and of those 6, only one fitted to a Kia Sorento does not auto switch off for a day or more. The Jag switches on once a day at the same time every day, so clearly some thing in car switches on at that time, rest you see every two or three days it will switch on for a few minutes. Kia it seems cold affects the battery and depending on temperature it switches on for maybe 2 minutes at today's temperature 4 times an hour.

The only reason I take batteries off charge is 6 batteries and two chargers.

There was a comment about checking voltage under load and after use.

Prior to use was 12.8V
Run under full load Voltage drops to about 9.8V
When load ceased (after several minutes) new steady-state was 12.4V

9.8 volt under load seems rather low, yes for old cars 9 volt at cranking was OK and we used 9 volt ignition coils with a resistor which was shorted out at cranking so voltage did not drop to coil, but normally with a load like a winch we would expect to see at least 11 volt, as it is a sustained load. Other voltages OK, so maybe battery too small for winch?

Battery ‘was’ fine, at 9 yr old now showing its age I guess.