Deep Cycle Battery - Tests Good, Functions Bad…

[Bolster]

I have a 120Ah deep cycle battery I keep in the garage, connected to a NOCO 7A smart charger. The deep cycle battery gets used during (increasingly frequent in california) power outages, to charge phones, charge tool batteries, and run LED lights when the power’s out, or whenever I need a DC source. It’s 4 years old, and is wired with a low voltage disconnect. Recently, while using it in conjunction with a Milwaukee M18 DC charger, I noticed the low voltage disconnect activated halfway through a charge of a 3.0Ah battery. (And the deep cycle battery was hooked to the charger at the time! So was getting constant input!) That’s weird. A 120Ah battery (on the charger!) is having difficulty charging a 3Ah battery? So I charged the deep cycle overnight with the NOCO to 100%, then took it down to the local auto store for a load test, where it tested “good but needs charge.”

Seems to me, what I’ve got, is a battery that charges and tests “good” but doesn’t have much capacity. Does this make sense, can someone explain what’s happening here?

Should I get a hydrometer to investigate further? Should I put a load on it and see how long it’ll run before the LVD activates? Or what do you suggest? What’s got me confused is “testing good.”

 

[Showkey]

If it’s an AGM hydrometer will not work. Wet cell hydrometer will confirm each cell. Will also confirm each cell has enough water. Might have one or more bad cells.

First check monitor voltage during charging sequence. Suspect the NOCO smart charger has a problem ? Looking for 13.5-14.5 depending on what charging profile is being used by the smart charger.
Second check would be battery voltage check several hours after charging. Looking for 12.8 or greater.
Third check apply a load and monitor voltage.

 

[Shiftless]

Showkey has good advice. to that

Did you ever run that battery all the way to dead and not recharge right away?
Sulfation kills a lot of batteries.

4 years old is not all that old. I have two 75 AH batteries I keep for the same reasons as you. I need back up for my sump pump as well as during Red Flag Day PGE scheduled shutoffs. I have 2 inverters. The big one is 1000 watts. I have a 2 amp smart charger for maintenance and a 10 amp charger for recovery after use.
I generally replace these batteries after 5-6 years even if they have seen minimal use. My neighbor has a non critical use for my old ones...12 volt lights in his backyard storage shed

 

[Bolster]

I shoulda given more background info, sorry:
- No, never run dead, not even close. Installed a LV disconnect when I bought the battery for just that reason, but it sits on the NOCO smart charger all the time, except when pulled into mobile use, and then the LVD monitors discharge. The LVD has only tripped recently, as described above.
- It's not AGM, it's your typical lead acid wet cell battery, but deep cycle-ish, called a marine/RV battery. Energizer 29HM from Sam's Club.
- I monitor the electrolyte, it always covers the top of the plates.

Will do Showkey's tests and report back, thanks. Agree...4 years is not very old for a deep cycle. Darned PGE Red Flag Days, anyhow.

PS: This charger: https://no.co/g7200

 

[Bolster]

Looking for 13.5-14.5 depending on what charging profile is being used by the smart charger.

Spent a while taking measurements: [EDIT: these measurements taken after the battery had been sitting on the smart charger for hours].

The voltage goes into the battery (when the 25%, 50%, and 75% lights are lit on the charger) in falling spurts...high to low, then repeat. On average, the higher part of the readings is 14.3V then falling to 13.7V before repeating. (The highest number I saw, only for a brief moment, was 15.1V; the lowest, 12.9V).

Once the "100%" light is lit on the charger, there's an audible click, and the voltage hugs a slowly falling range from 13.2 to 12.6V. Meanwhile the 100% light is lit. Once the voltage falls below 12.6V, the charging cycle (25-50-75 lights) begins again.

It takes about 4 minutes to complete the whole cycle from the start of "25%" to the end of "100%."

Does this help with the diagnosis?

 

[MattT]

It sounds like your battery is shot. 4 minutes to charge with a 7A charger isn't nearly long enough. Then rapidly self discharging unless the charger is pulling it down. You could try disconnecting the charger immediately after it hits 100% and clicks to rule out it discharging the battery.

That said the chargers behaviour is also a little odd. Do you have another, preferably larger and "dumb", charger you could try?

 

[Showkey]

Charging sequencing seems odd. Full charge float or pulse charge should be 12.8-13.0 volts.
The fact the battery is dropping so quickly is a concern. Then the charger is start a new charge sequence. Suspect one or more cells are open or shorted ?

Disconnect the charger after it says 100% leave the battery sit for 12 hours. Measure the voltage .......static resting voltage it should be above 12.8.

4 years on that battery in a “hot” climate is a very common failure time.

 

[Tracs]

As someone who has replaced a fair share of batteries living in a -30 climate I can tell when batteries are on the way out or done. Yours sounds done. 4 years might seem a short period, but batteries these days just don't last.

I had a battery that did the same thing. Smart charger charged it fast, said it was 100% and drained almost instantly in a vehicle.

 

[Captain Spaulding]

That’s basically how most deep-cycles fail. After the first few cycles, every charge/discharge cycle reduces the battery capacity a little bit. Eventually it gets to the point it’s too small for the job.

Your charging and post charging voltages sound close to right. Most flooded cells are full charge at 12.65V, so when you unplug the charger the battery will hold the charger float voltage for a while, then fall to the battery OCV. The difference between 12.6 and 12.65V is big though, so be sure to get accurate measurements.

Trojan golf car batteries are excellent deep-cycle batteries. T1275 is a nice one in 12V, or you can use two 6V batteries for increased capacity.

 

[theoldwizard1]

First, I don't care what the label says or what anyone tells you, "dual purpose"/"marine" are NOT true deep cycle batteries ! The most cost effective, lead acid, true deep cycle batteries are golf cart batteries. These are typically flooded (liquid electrolyte) and 6V with the following exception.

Trojan golf car batteries are excellent deep-cycle batteries. T1275 is a nice one in 12V, ...

The standard Trojan 6V golf cart battery is a T105. Both of these are available in AGM ($$$). The only place you will find these batteries is at a golf cart distributor or a solar power store.

For good, reasonably price 6V golf cart batteries, shop Costco or Sams Club. Under $100 ea.


No hard "proof", but I am of the opinion, that batteries should NOT be left on ANY KIND of charger 24/7 for days on end. Plug you charger into a cheap wall timer and set it to run no more than 8 hours in a day. It you discharge your battery (no more than 80% for non-deep discharge and 50% for true deep discharge), manually turn the lamp timer on.

 

[Bolster]

Thanks for the help, folks. I took the charger off tonight, we'll see where it is in 12 hours. I agree with the consensus: I have a dying battery.

Showkey said: "4 years on that battery in a “hot” climate is a very common failure time." My battery lives in the garage, and during the summer, sometimes it reaches 110 degrees. So maybe this is a normal lifespan for a heat-abused battery.

Now regards leaving the battery hooked to a smart charger: I've heard both sides of that argument, both pro and con. I personally don't know. On internet searches, I find mostly pro:

“These Smart Battery Chargers have three distinct operating modes: BULK, ABSORPTION and MAINTENANCE…..You should leave the charger operating in this MAINTENANCE mode as long as possible….Please note that the MAINTENANCE mode is NOT a trickle mode, the charger will issue zero current if the battery accepts proper charge during the charging process. This feature allows the charger to be connected indefinitely….You may leave the charger connected indefinitely. It will not overcharge (or trickle charge) your battery…The Smart Battery Charger does not have any timers. All decisions are based on the battery voltage/current. ”

http://www.a-aengineering.com/chargeroperation.htm

“You should have no problem setting this battery charger and leaving it for months on end, unattended. The CTEK [Smart Charger] Battery Chargers work very differently than the old, traditional battery tenders. The old tenders used a trickle charge. Basically they constantly applied a little bit of power. This wastes electricity and can lead to some lead acid batteries overflowing, which is a big problem. The CTEKs do not trickle. Instead they detect when the battery has lost some charge. Then the charger kicks on, tops off the battery charge, then kicks over. Not a constant trickle like the old style tenders. These charges are very popular among car collectors that have antique or high end cars that spend most of their time in a garage. They hook the charger up to the car and let it sit. That way on those particularly nice days, or special occasions their treasured car fires right up and the battery is kept in good condition.”

https://www.etrailer.com/question-13617.html

This memory capability along with the zero-overcharging feature means you can safely leave this [NOCO] charger connected to your battery for long periods of time.

https://www.toptenreviews.com/car-battery-chargers-noco-review

Our chargers don´t need any specialist knowledge and they can be safely left connected for long periods of time – even months – as they keep your battery maintained.

https://www.ctek.com/education/car_battery_charger

The charger can be left connected to the battery indefinitely.

--NOCO manual

 

[HOTFR8]

Sounds like it can no longer hold a load.

 

[HenryAZ]

I have seen this behavior when the internal resistance of a battery gets very high. The surface voltage is good, but the resistance (usually due to sulfation) only allows minimal amps to be passed through. This could also explain the trouble with charging it. A battery tester that shows internal resistance is a good thing to have. I use an Ancel BA101, but the Foxwell BT705 is also highly regarded.

 

[Showkey]

Thanks for the help, folks. I took the charger off tonight, we'll see where it is in 12 hours. I agree with the consensus: I have a dying battery.

Showkey said: "4 years on that battery in a “hot” climate is a very common failure time." My battery lives in the garage, and during the summer, sometimes it reaches 110 degrees. So maybe this is a normal lifespan for a heat-abused battery.

Now regards leaving the battery hooked to a smart charger: I've heard both sides of that argument, both pro and con. I personally don't know. On internet searches, I find mostly pro:

“These Smart Battery Chargers have three distinct operating modes: BULK, ABSORPTION and MAINTENANCE…..You should leave the charger operating in this MAINTENANCE mode as long as possible….Please note that the MAINTENANCE mode is NOT a trickle mode, the charger will issue zero current if the battery accepts proper charge during the charging process. This feature allows the charger to be connected indefinitely….You may leave the charger connected indefinitely. It will not overcharge (or trickle charge) your battery…The Smart Battery Charger does not have any timers. All decisions are based on the battery voltage/current. ”

http://www.a-aengineering.com/chargeroperation.htm

“You should have no problem setting this battery charger and leaving it for months on end, unattended. The CTEK [Smart Charger] Battery Chargers work very differently than the old, traditional battery tenders. The old tenders used a trickle charge. Basically they constantly applied a little bit of power. This wastes electricity and can lead to some lead acid batteries overflowing, which is a big problem. The CTEKs do not trickle. Instead they detect when the battery has lost some charge. Then the charger kicks on, tops off the battery charge, then kicks over. Not a constant trickle like the old style tenders. These charges are very popular among car collectors that have antique or high end cars that spend most of their time in a garage. They hook the charger up to the car and let it sit. That way on those particularly nice days, or special occasions their treasured car fires right up and the battery is kept in good condition.”

https://www.etrailer.com/question-13617.html

This memory capability along with the zero-overcharging feature means you can safely leave this [NOCO] charger connected to your battery for long periods of time.

https://www.toptenreviews.com/car-battery-chargers-noco-review

Our chargers don´t need any specialist knowledge and they can be safely left connected for long periods of time – even months – as they keep your battery maintained.

https://www.ctek.com/education/car_battery_charger

This pretty much sums up the chargers and the capabilities of the better ones.
As seen these battery and maintenance chargers threads are like oil threads.

Seems like the charger and timer defeats the anti sulfation and pulse/float programed features.

Example:
In prior home had a battery backup basement sump pump. It had to be charged and ready. The supplied “charger” cooked the battery in two years. Swapped with quality maintainer, ( aka smart charger) problem solved to a 5 year battery life with excellent performance when needed. But still swapped the battery at five years as a precaution......has this pump needed to run if the power is lost !!!!

 

[Bolster]

Disconnect the charger after it says 100% leave the battery sit for 12 hours. Measure the voltage .......static resting voltage it should be above 12.8.

12.5V after 12 hours off the charger. So, I guess that's the answer, isn't it. I think I will skip the load test...no reason for it, and no baseline to compare to. Time for a new battery!

Thanks for teaching me how to diagnose!

Still curious how a fancy mechanic's purpose-built battery tester* would diagonose the battery as "good." That's odd. But thanks to the fine folks at GJ, I don't need the say-so of a battery tester anymore; I can diagnose it myself.

What I will do differently for the next battery:
(1) establish some baseline measures, such as how long a certain load can be on the battery before the voltage drops 0.2 or something like that;
(2) will explore the idea of bringing the battery inside the A/Cd house during hot summer. I know you're not supposed to charge a lead-acid in the house though...

PS: The NOCO charger has a "boost recovery" mode on it I've never tried...will give that a shot before exchanging the battery, and will report back on any progress made...

* = I wonder if the auto store tester was a conductivity/resistance tester, not a load tester. I've read that the conductivity/resistance testers can give a green light to dying batteries...

 

[Showkey]

Think 4 years is about the average these days. Obviously if the average is 4, then many get 6-8 years and some get 2.

Doubt the A/C home storage would move the number much. Hot climate deterioration is Texas and Arizona with under hood temps consistently near 200*. That environment tends to bring the average down. I have large AGM in “cold storage” all winter. No power available to charge. Disconnected from the RV so there’s no parasitic draw. Temps range from -25* to 50* for 5 months with average 28* +/- 15. Connect and starts a diesel every year in spring. Use to bring it home, found there’s no need. Cold is your friend as long as the battery is charged.


As far as the electronic battery tester........if the battery is “fully charged” when tested and the result is charge and retest ..........the tester is confused by the data and it’s warning sign.....the end maybe near. The testers are bias to not show bad when the numbers really should show weak.......the default is charge and retest. This is especially true if there’s one weak cell.

 

[American Locomotive]

Your battery has lost capacity, but still delivers acceptable current. The tester at the store is just likely looking if it can deliver a certain amount of amps for a couple of seconds. If it can do that, the battery passes. They aren't doing a long-term discharge test.