Sealed Lead Acid Battery Information

I gathered the informtion below from alot of different places on the internet and have put them together in a way I hope will be informative for the user at large. It should be noted that the cycle lifes stated are for general purpose batteries which are the ones commonly used because of low cost.

Some batteries like the B&B Batteries EB Series of batteries are made for high cycle life with deep discharge and will provide more cycles then standard batteries when used for electric transportation needs. The voltages listed below are still valid for all SLA batteries.

This Information is for Sealed Lead Acid (SLA) Batteries Only:

12 Volt batteries have 6 cells each
24 Volts = 12 cells
36 Volts = 18 cells
48 Volts = 24 cells
Fully charged cell voltage = 2.1 Volts
Nominal cell voltage = 2.0 Volts

The recommended end-of-discharge voltage for sealed lead-acid is 1.75 Volts per cell. The discharge does not follow the preferred flat curve of nickel and lithium-based chemistries. Instead, Lead-acid has a gradual voltage drop with a rapid drop towards the end of discharge.

The sealed lead-acid battery should not be discharged beyond 1.75 Volts per cell, nor should it be stored in a discharged state. The cells of a discharged lead-acid sulfate, a condition that renders the battery useless if left in that state for a few days. Always keep the open terminal voltage at 2.10 Volts and higher.

The cycle life of sealed lead-acid is directly related to the depth of discharge. The typical number of discharge/charge cycles at 25°C (77°F) with respect to the depth of discharge is:

* 50 - 100 cycles with 100% depth of discharge (full discharge)
* 150 - 250 cycles with 70% depth of discharge (deep discharge)
* 300 - 500 cycles with 50% depth of discharge (partial discharge)
* 800 and more cycles with 30% depth of discharge (shallow discharge)

Cycle life measured until 80% of original capacity can no longer be recovered by charging.

now all we need are performance charts by temperature.

OPERATING TEMPERATURE: Batteries work best within a limited temperature range.

Most wet-cell lead-acid batteries perform best around 85 to 95 F.

At temperatures above 125 F, lead-acid batteries will be damaged and, consequently, their life shortened.

Performance of lead-acid batteries suffers at temperatures below 72 F;

the colder it is the greater the degradation in performance. As the temperature falls below freezing (32 F), lead-acid batteries will act sluggish - the battery has not lost its energy; its chemistry restrains it from delivering the energy. Batteries can also freeze. A fully charged lead-acid battery can survive 40 to 50 degrees below freezing, but a battery with a low state of charge (SOC) can freeze at temperatures as high as 30 F. When the water in a battery freezes it expands and can cause unrepairable damage to the cells.

I can personally attest to the fact that at 95 degrees the batteries have a large amount of extra power over even 80 degrees and by the time you get down to 70 degrees (like now) it feels like you are riding a much less powerful bike. (assuming I'm not experiencing other problems)

Thank you for gathering this information on SLA batteries.

Is the depth of discharge determined by the voltage of the battery when not under any load?

I have an idea as how to limit the depth of battery discharge. How can I control the temperature, ride inside, move to somewhere along the equator?

Dalecv said:

Is the depth of discharge determined by the voltage of the battery when not under any load?

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Your controller is likely going to sense the lower voltage while under load and try to cut out. If you back off then the power comes back on again. I never drain the battery that low and so my batteries are probably 4-5 years old now and still working okay. (I bought them wholesale and they were probably already a few years old when I got them) By never draining the battery very deeply it seems to make the battery last a lot longer, but I'm afraid that time itself is an enemy you can't avoid. There is a fairly constant deterioration rate just based on time.

Voltage is tricky for establishing depth of discharge because every battery seems to have a slightly different baseline voltage. Mine tends to run a little higher than most other descriptions of SLA I've seen. I'm still (after two years) starting rides at 13.0 volts and ending rides at 12.2 volts, which is higher than most numbers I've seen listed. The controller will allow a voltage as low as 10.0 volts which seems completely unreal of a target to shoot for. (my batteries would be better off with a 11.5 volt cutoff based on the performance I've seen)

Thanks safe, on my EbikeE most of my rides only discharge the batteries to the 48 volt level when under load, I did do 25 miles one ride and was down to 44 volts during heavy load starting the bike from a stop. This is my primary bike and I want the batteries to last and from the chart they should do so.

My Bike Friday only has 36 volts with 18 Ah and those batteries fall below 36 volts pretty easy.

So it sounds like to get good life out of SLA batteries one needs to have more volts and amp hours than needed for the expected commuting distance and carry a charger so they can be plugged in whenever possible.

Dalecv said:

So it sounds like to get good life out of SLA batteries one needs to have more volts and amp hours than needed for the expected commuting distance and carry a charger so they can be plugged in whenever possible.

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Yes indeed. In many cases, SLA is more expensive than other chemistries over a 5 year timeframe.

I'm not a convert yet, my first money is on SLA, but when they get weak we will see where I go next. Hopefully to the hypercapacitor.

From Battery University:

Finding the ideal charge voltage limit is critical. Any voltage level is a compromise. A high voltage limit (above 2.40V/cell) produces good battery performance but shortens the service life due to grid corrosion on the positive plate. The corrosion is permanent. A low voltage (below 2.40V/cell) is safe if charged at a higher temperature but is subject to sulfation on the negative plate.

Depending on the depth of discharge and operating temperature, the sealed lead-acid provides 200 to 300 discharge/charge cycles. The primary reason for its relatively short cycle life is grid corrosion of the positive electrode, depletion of the active material and expansion of the positive plates. These changes are most prevalent at higher operating temperatures. Cycling does not prevent or reverse the trend.

The optimum operating temperature for the lead-acid battery is 25°C (77°F). As a guideline, every 8°C (15°F) rise in temperature will cut the battery life in half. VRLA, which would last for 10 years at 25°C (77°F), will only be good for 5 years if operated at 33°C (95°F). Theoretically the same battery would endure a little more than one year at a desert temperature of 42°C (107°F).

So on my bike the charger would reach 14.7 volts (2.45 V/cell) which is considered high.

The garage temperature was often 90-95 degrees.

At 2,500 total miles and a typical ride being 10 miles long that means I did roughly 250 cycles... about what you would expect.

In the end the heat seems to be the most significant "threat" to your battery based on this information.

I think a good charger also plays into the equation for SLA batteries and why I bought a Soneil from, http://www.batterystuff.com/battery-chargers/48-volt/all/Son4808SRF.html
So not only is my money in SLA batteries but a charger as well. :?

It does recharge the batteries pretty quickly compared to the one I received with the Goldenmotor kit on my Bike Friday.

Good chargers do play an important role in sla life. They can also play tricks on you in a warm charging enviornment if you don't pay attention with a voltmeter.

Some chargers shut down when the temperature gets to high as a precaution to not destroy battery and or charger. and it may shut down leaving one to think the battery is fully charged when it really isn't. After charging allways check with a voltmeter to make sure the batts have attained a full charge. I had a charger that did this and it wasn't a cheap one.The reason I found out was after a long ride and putting the sla on the charger it went to green too quickly I thought.I checked with a voltmeter and found they were only half way there.I unplugged the charger to reset it,plugged it in again and finished the charge. This only happened in summer months with temperatures above 90deg.F. otherwise the charger worked like a charm.

Eric

Eric G said:

After charging always check with a voltmeter to make sure the batts have attained a full charge. I had a charger that did this and it wasn't a cheap one.

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I think the prices must have gone down, or you bought a specialized charger to match your bikes voltage. (custom is always more expensive than generic) If you seek out a computer controlled, digital readout, multistage (desulphate, main charge, declining charge, float charge) generic 12 volt automobile charger with adjustable current settings they can be had these days for about $25. I suspect people get themselves into trouble when they buy custom chargers that are, say, 36 volts or 48 volts so that they don't have to undo their wires when they connect their charger. For me I used the old:

"Switch from serial to parallel when I charge trick"

...and that allows me to charge my 36 volt system with a 12 volt charger.

You definitely can go a lot cheaper if you go generic...

Yes Safe it was a "Specialized Charger" 12volt 3 stage
(bulk,absorbsion & float) microprocesser controlled AGM Battery charger with over heat protection.I use a Cheap 36 volt 2 amp charger for on the road.(opportunity charging).

When I noticed the problem of heat shutting down the charge I ended up taking the batteries and charger into an air conditioned enviornment. It charges up to 14.4 volts (bulk) stays at 14.4 for a while (absorbsion) and then a float voltage of 13.5v with a special waveform where the voltage spikes to ~14.1 volts and when the voltage drops down again to 13.5 it'll spike again and so on...

All I'm saying is,is to pay attention to your charger,don't allways assume that all is fine.After a while you get a sense of knowing how long it'll take to charge in relation to the battery's state of charge or the length of ride you've done.After a while you sorta get a feel for it,if that makes any sense?

Anyhow Fall is definatelly on the way with the temps dropping and this heat thing won't be an issue til next summer.Now I just gotta deal with lack of performance until next spring...LOL

Eric