Optimizing the life of lead-acid batteries

[lightseeker2009]

What can you do to prolong the life cycle of sealed lead-acid batteries? For example the small 6V types you get in lanterns, and the 12v types you get in jumpstart assistance packs for cars.

Will a cheap automoble charger actually decrease the life of these batteries? Will a better, ''inteligent'', charger prolong the life of such batteries.

[Gregozedobe]

Not deeply discharging, recharging as soon as possible after use, using a decent intelligent charger (3-5 stage), don't use a cheapo "float" charger that will overcharge the battery if left connected for too long, storing battery at normal room temps, charge voltage adjusted for battery temp, adding distilled water as level goes down (many "sealed" batteries aren't designed for maintenance, but some can be opened - not applicable to Gel/AGM type).

Yes and Yes (although it is more a function of design rather than purchase price).

[lightseeker2009]

Thanks

[Ray_of_Light]

Sealed Lead Acid batteries (more properly, Valve Regulated Lead Acid batteries, as they are not truly sealed) comes in two classes: AGM and GEL. The first class, which is more diffused but not necessarily the cheaper, has the electrolyte embedded in an Adsorbent Glass Mat, while in the second the electrolyte is suspended in a gel of fumed silica. AGM batteries have a lower internal resistance, GEL have a better cycle life.
Among those two wide classes, there are different types. Starter batteries are made with many thin lead plates to allow the delivery of strong current, but they have a limited life cycle; leisure, marine and traction batteries, also called deep-cycle batteries, have few thick lead plates to withstand the continuous cycling. Data sheet from manufacturers, or seller websites, usually specifies if the battery is for starter use or deep cycling. There also is another category, called standby batteries, which are designed to remain in standby for most of their lifetime, like UPS, alarm panels, emergency illumination. Lead acid batteries which are never cycled suffer of positive plate growth, which ultimately shreds in dust, making the battery bulge and go out of service. These standby batteries have a percentage of phosphoric acid in the electrolyte, and they reach the nominal capacity after one year they are connected to the float charger.
You cannot increase the cycle life of any given SLA lead acid battery above 200 cycles at 100% DOD; you can only extend, often extensively, their calendar life. Those sealed lead acid batteries are recombining type batteries - which relies heavily on the oxygen cycle to recombine water. The oxygen cycle is what ultimately kills batteries connected to a float charger, as this cycle consumes more energy than what is stored chemically in the battery.
The tricks to extend calendar life of SLA batteries is to cycle them 70% DOD every three to six months, keep them at 20 °C, and use a microcontrolled pulse charger like the Optimate 4. Or, like I do, keep them on the float charger for one day every month, and cycle them every six.
Another hint. SLA AGM batteries are not all the same. The quality of the battery is determined mainly from the fibre size of the separator and from the plate pressure; it ranges widely from cheap imports to the Odissey brand. If you have a good SLA lead-calcium battery, like CJB, Yuasa, FIAMM, it can last with proper care for over 15 years, just like pure-lead wound Cyclon batteries. Even when neglected, those battery can easily recover from complete sulfation with a simple procedure.
In my jump starter, I replaced the cheap 12 V 18 Ah OEM battery with an hi separator pressure AGM batteries designed for golf caddies and, ten years after, it still delivers the same current with the same capacity.
6 V 4 Ah type batteries exists in many different flavours, and their life is based on their quality and the accuracy of the float charger built in the lantern. Good types can also be serviced every five-six years.
Last thing: use the cheap automobile charger only with liquid electrolyte car batteries; it will kill any sealed lead acid batteries in matter of days.

Regards

Anthony

[Lightfoot98]

......... those battery can easily recover from complete sulfation with a simple procedure.

What is that simple procedure??

[Ray_of_Light]

What is that simple procedure??

The VRLA batteries are subject to three principal failure modes. Any early failure is technically named PCL (Premature Capacity Loss).
The PCL-1 mode is caused from developing a passivation layer between the positive grid and the active material deposed on it. This has been solved by adding tin, silver or both to the positive plate, which act as a dopant.

The PCL-2 mode is another type of interconnecting layer failure; some PbO forms at the interface between the PbO2. PbO is a semiconductor which impede the recharging of the battery. This is more common in pure lead plate configuration (think of Cyclon / Enersys / Exide batteries).

The PCL-3 failure mode is the polarization of negative plate. This is when the oxygen cycle, necessary to recombine water in a sealed battery, becomes too strong. Normally, oxygen lands on the negative plate forming PbO, the H2SO4 electrolyte convert it to PbSO4, and then is treated as a the normal discharge product of a negative plate, effectively reforming water. Problem is when any charging current flowing thru the battery initiate the oxygen cycle, due to lowering of overpotential caused from impurities or overcharge.

There are other failure modes, and those are EOL modes (End Of Life), namely electrolyte dry-out, gravity stratification, plate shredding, negative top lead corrosion, negative plate dendrites. There is no indication of sulfation as a failure mode of a battery, as it is a normal phenomena.

How to recover? Recharge the battery. If any of the other PCL modes are not present, sulfation can be easily recovered.

Traditionally, a sulfated lead acid battery had to be left under float charge for months, in order to recover some capacity. Lately, better methods have been devised. Lead sulphate is a normal discharge product, initially slightly soluble in sulphuric acid. If the battery is left uncharged, the lead sulphate crystallise, converting from an amorphous state to a crystalline state. Since it is non-conductive electrically, battery doesn't seem to accept charge. In reality it will, in the range of few microamps, this is why will take months. The actual trend is to use high energy pulses, which produces a mechanical force that, in turn, fracture the sulphate crystals. The pulse has to have a current equal to the normal short-circuit current of the battery, and have a 1 microsecond duration every second. They uses large inductors and power MOSFETs.

If you type "desulfator" into Google, you will see a large offering of those gizmos. They are not officially endorsed by battery manufacturers, but they works. Due to the large market created from solar energy installations, which have to deal with chronically undercharged batteries (which are perennially sulfated), a desulfator proves a wise investment. Desulfator techniques are also used in specialised charger, like the Optimate4, which I use to keep charged and clean from PbSO4 the motorcycle batteries installed in my UPS (I don't use VRLA batteries for this purpose).

The real problem comes when the sulfation is aggregated to other PCL modes. The most common combination is Sulfation/PCL-2. Even this can be recovered, but you need to open the battery, as only dendrites and plate shredding are unrecoverable. If there is enough interest, I can prepare a recovery tutorial and present in its own thread.

Hope this helps.

Anthony

[Lightfoot98]

I see no simple procedure!

Please elaborate the procedure.

Thanks

[Ray_of_Light]

1. Buy or build a desulfator of the right size for your battery capacity. Actually you can only buy desulfators for 12 V batteries.

2. Connect it to the sulfated battery.

3. After a week, if no other failures are present, the battery will be able to accept charge from a standard charger. Capacity will be low. If the battery will not accept charge, there are other failures. You need to recycle the battery.

4. Reconnect the battery to the desulfator. It may take up to two months to gain the complete capacity.

Anthony

[malow]

and... "how" the desulfator... desulfate?

edit:? google-ing a bit show that most cases it actually works well, but some don't.

http://www.reuk.co.uk/Battery-Desulfation.htm

[pavithra_uk]

Prevent deep discharge, short circuits, shock & vibrates
Keep low temp as much as you can.

If you charged (or keep float charged constant voltage) below 13.6V, battery will last longer. many float charger use 14.4V constant voltage that can lead to positive plate corrossion.

I found lot of rechargeable lanterns that using 6V SLA batteries can cause loss of electrolyte (Do not think these are 100% sealed) because of they charging near 8V long time.

Personally Im doing these for extend my battery life:

1. Charging current limit
2. Constant voltage charge limited to 13.3V
3. After 1 day of Constant voltage charge, remove charger.
4. Occasional topping charge
5. Recharge only if battery used.

[filibuster]

...In my jump starter, I replaced the cheap 12 V 18 Ah OEM battery with an hi separator pressure AGM batteries designed for golf caddies and, ten years after, it still delivers the same current with the same capacity.

Anthony, what brand and model did you settle on for your "hi separator pressure AGM batteries designed for golf caddies"?

[deadrx7conv]

I use a BatteryMinder desulfator charger. I've also used the 15w solar panel desulfator/charger to bring completely dead marine/rv/auto batteries back to life.

[tony22]

Or, like I do, keep them on the float charger for one day every month, and cycle them every six.

Ray of Light, does this recommendation still hold true if the battery is rarely used? I have a 5.5Ah sealed lead acid that powers a lamp, but the lamp is rarely used. What are the self discharge characteristics of a SLA?

[jayflash]

Five stage charger? Let me count: #1 CC; #2 CV; #3 discharge/test?; #4 desulfate?; #5 CC (float) again? Is that close to what a five stage charger might provide?

I've a collection of SLA's & three UPS units. The stored batteries got topped off twice yearly to about 14.5v. The UPS units self-test, plus I disconnect them once yearly. For the past couple years I've discharged the stored SLA's @ .5A until 11.5 - 11.8 volts are reached. These are 7Ah to 9Ah capacity and test from ~3Ah for a 10 year old, to over 5Ah for the new batteries. I'm sure another couple Ah are available down to 11 volts.

Is it better to exercise the SLA's more often and should I swap the UPS batteries and desulfate them on a schedule? I should really test their float voltage, and may have a problem with one UPS -- it shuts down during disconnect after about 7 minutes even though it indicates 30 minutes are left. The overload light comes on and it turns off. Still, it self and manual tests good.