Lead Acid battery trickle charger pumping out 15.8 volts

[Dabbo56]

Just bought an Energizer battery trickle/maintenance/conditioner for old-fashioned vented 12V lead acid battery. The battery is in reasonable condition and recently charged. My DMM says 15.8 volts, and I’m a bit alarmed. I was expecting a max voltage of 13.8 to as much as 14.4 volts. Should I be concerned?

[tunk]

Is it 15.8V when connected to the battery, or when nothing is connected?
If it's the latter and it's an old type transformer-based charger, then it may
be ok, as the voltage will drop with a load.

[Dabbo56]

It’s 15.8 v across battery terminals

[bdunham7]

What model of charger is it?  Do you have a manual?  It is possible this is some initialization, test or equalization cycle, but if that is the continuous voltage across a good battery then it is cooking it, which is all bad. 

How big is the battery?  Do you have a way of accurately measuring current?

[AVGresponding]

Also worth asking if the DMM is reading correctly...

[DavidAlfa]

Ensure the DMM batteries are good!
Mine usually starts reading waaay higher when the lo-bat symbol appears yet I keep using like that for months....
Until I measure 7V from a USB port like few months ago.
Survived the cardiac arrest, replaced the batteries, 5.16V 

[Dabbo56]

Described on Amazon as: “ Energizer 4 Amp Fully Automatic Smart Charger, 6V & 12V Battery Charger, Portable Trickle Charger, Battery Maintainer (Charges, Maintains & Reconditions Car, Motorbike, Caravan, & Motorhome batteries)”.
It has an integral voltmeter which agrees with my DMM, which is known to be accurate-ish and agrees with my other DMM.
The user guide talks about 9 stages to the charging cycle that it rotates through, but it’s mostly marketing guff.
I’ve just checked again after a few hours and it’s still at 15.8 v across battery.
I have 2 other batteries on trickle with other units and they are at 13.8 and 13.6 volts.
My plan is to see if it destroys the battery. When I get a chance I’ll insert an ammeter. Will update as and when 🤞

[thm_w]

Too high if its stabilized at that voltage. They claim its a smart charger: https://www.energizerpower.com/product/enc4a/
So a good charger might temporarily spike to that level but should drop to ~14V after its fully charged.

Battery might be dead too, even though you think its in reasonable condition.

edit: yeah the charger probably thinks the battery is sulfated and is trying to recover it. https://www.crownbattery.com/news/sulfation-and-battery-maintenance

[Dabbo56]

It’s the next day and the voltage has stabilised at 13.8 volts. The battery is warm to the touch but appears unharmed. I disconnected the charger and put the headlights on for 30 seconds and voltage still in the mid 13 volt region.
Just for fun, I’ve taken an old motorcycle battery off the shelf which I removed over 5 years ago. It still registered 4 volts. I’m not expecting a miracle but curious to see what the charger does to it. Will keep you posted

[Geoff-AU]

could be an equalisation charge

https://www.morningstarcorp.com/lead-acid-batteries/

[floobydust]

I had purchased the smaller Energizer ENC2A (7-stage, 2A). It's a good quality hardware build but the firmware sucked badly. It was super finicky about initiating and continuing charging. I tried it on a few old gel-cells and it went to ERROR or just bailed too easily. I took it back and got a refund because I need a charger to, well, uh charge instead of wrongly concluding there is a battery problem. So I'm saying the firmware is too smart for itself. No sign of an equalization phase. The owner's manual reeks of a foreign language:

"The {ENC4A} charger uses a proprietary 9-stage charging process designed to optimally charge and maintain batteries. (The below chart and illustration show the charging routine when charging a 12V deeply discharged battery in mode 3)"
Stage 1 - Diagnosis: Analyze if the battery can accept a charge or not, and then prevent charging from proceeding on the a defective battery;
Stage 2 - Desulphation: The charger can rescue most drained batteries with voltages up to a Min 1.5±0.5V
Stage 3 - Pre-charge: If the battery voltage is less than 12V, charge it at the smaller current, which will protect the battery better;
Stage 4 - Soft start: Charge the battery to the maximum current gradually and never suddenly.
Stage 5 - CC1/CC2/CC3 (Constant Current): The charger automatically adjusts the current according to the battery status in constant current, which benefits the battery for a long life;
Stage 6 - CV (Constant Voltage): The battery is charged to nearly full, and will top off at 14.6V DC;
Stage 7 - Resting: The charger will cut off with full charged statement, and achieves the high energy efficiency;
Stage 8 - Recond: When it is fully charged and low to 12.8V within 2min, the charger will judge automatically.
Stage 9 - Restoring: The charger monitors a fully charged battery automatically. If the battery falls below 12.8V DC, the charger will restart from stage 3 to stage 6.

[thm_w]

Not saying this is definitely the case, but, if they are old cells they probably are bad (<20% capacity?) and not useful in most common scenarios.

Do you recall what voltage they were at? Or measure the capacity and ESR if you are able to.

[floobydust]

As I remember, the dud gel-cell had one cell that was high resistance and weak, not shorted. So with no load, terminal voltage was low around 10V it looked OK, but charging it you could not put much current into it. That seemed to crater the Energizer firmware. It seemed to be confused that 10V was a dead battery and charging it jumped to 14V instantly with low charging current and it said "ERROR". Other times it just would not stay charging.
It was too finicky. There was no hazard. Just the software confused by a battery that appeared instantly charged lol.

[thm_w]

Yeah its not a hazard, but that battery is basically useless for most applications.
Measure the Ah if you can. The lead acids I had checked from storage that were 10-10.5V, I don't remember measuring much if anything, the 11V discharged were down to <40% original capacity.

[dietert1]

Recently an expensive patient simulator Fluke Index II that we have for more than 15 years would no longer turn on. It has a 12 V, 2 AH lead-acid battery inside and came with an external charger. After renewing the battery i watched a little closer what the charger did and finally opened it to discover a switchmode supply with MCU control inside, with enforced cycle charging. It wouldn't support a 13.8 V trickle mode, but impose cycles onto the new battery, also with voltages of more than 15 V.
Replaced it by a little  transformer-based supply that sustains a stable 13 V up to 500 mA. Consumption of the simulator is about 150 mA. Hope the new battery will live forever..

Regards, Dieter