Sealed lead-acid batteries - delicate?

[poguy]

I know that deep discharge will kill SLA batteries and keep mine charged up. My main batteries for bicycle commuting was a couple 2 amp-hour 12 volt SLA from 1999. Worked great until one of them dropped on a cement floor. After that that one battery would sag under load. The other was fine.

To handle larger lights I went to a couple 5 amp-hour SLA's bought used at a hamfest. Both have early 2008 dates. Both worked fine until I dropped one on the same cement floor. (Too many things in my hands after changing clothes.)

I could not figure out what was wrong with them. I recently used one for bench testing a new setup. It heated up in one place. My guess is that either the electrodes or interconnect between cells was partially damaged. With a higher resistance it heated up under the 0.25 amp load.

Any ideas? I've heard a lot about SLA's, but nothing about fragility.

Related note: Are Li-ion cells delicate when it comes to physical shock? I'm thinking of switching to them.

 

[SilverFox]

Hello Poguy,

All batteries are sensitive to vibration or shocks that shift the battery internals.

Tom

 

[march.brown]

Sealed Lead-Acid batteries have a much shorter life than the ordinary Lead-Acid batteries ... Our very large capacity open 48 volt and 110 volt systems were all OK even after more than 20 years of use in a float system.

Unfortunately they needed a lot of maintenance with monthly topping up plus other jobs ... This kept two men busy all year round ... We had to carry out discharge tests every couple of years plus, as the cells got older, we had to remove the occasional internal short circuit on some of the cells.

We went onto the sealed cells and were able to put the two men onto other jobs ... The sealed cells were half the price and we changed them at the recommended ten years ... These systems had built-in internal impedance testers and an alarm would be given when the battery went out of limits.

So it might well be that your batteries were coming to the end of their life ... Car batteries don't last too long as they take a fair bit of punishment even with a good vehicle suspension system ... No lead acid battery, old or new, will pass a drop test onto a hard surface ... The plates and seperators are just not built for this sort of deceleration and will probably end up with internal short circuits ... I don't see any way of getting rid of an internal short circuit in a sealed cell, as you could on the large open-top ones that I worked on ... Your 12 volt battery is six small two volt cells, so it looks as though one cell of the battery has got an internal short-circuit ... Trouble is that you can't normally get to the straps that connect the individual cells together to make up the 12 volt sealed battery.

When you charge up the faulty battery, only five cells are working and the sixth might be seen as a resistor ... If you put a load on the charged faulty battery, you may well see a voltage drop if only five cells are active ... If you have a Voltmeter, you should be able to check this ... A 12 volt 6 Watt bulb on a couple of lengths of wire will be OK for a load and will take about half an amp drain ... Put your meter across the battery to check the on-load voltage.

I would consider replacing the dropped battery ... Our batteries floated at between 2.24 volts and 2.26 volts, so the initial 12 volt battery voltage after a charge should be about 13.5 volts then it would drop to a lower level ... It shouldn't sink below the 12 volt point though.

You might be better off using low self-discharge AA cells ... these are 2400 milli-ampere-hour capacity though only 1.2 volts each ... How many hours a day do you need the light to work for ? ... How many lumens do you need ? ... There are some good three AA cell LED torches about that should be OK for biking .. Some will attatch to your helmet.

Good luck with your testing and your biking.
.

 

[Mr Happy]

I recommend you take a variety of household items and drop them on a cement floor, then fill out the following table:

Dropped on cement floor      Damaged/not damaged?
-----------------------      --------------------
Vase
Clock
Television
Cups
Plates
Computer
Iron
iPhone
Watch
...

Look at the results and see if any kind of pattern emerges.

 

[march.brown]

I recommend you take a variety of household items and drop them on a cement floor, then fill out the following table:

Dropped on cement floor      Damaged/not damaged?
-----------------------      --------------------
Vase
Clock
Television
Cups
Plates
Computer
Iron
iPhone
Watch
...

Look at the results and see if any kind of pattern emerges.

.
I like this comparison ... Obviously written by someone with a sense of humour.

Since the battery contains a gel, I would suggest that the cup and vase be similarly filled ?
.

 

[TorchBoy]

And the clock. That would make it fun both before and after the drop test.

 

[dannstrait]

I accidentally shorted my 12V 8ah SLA battery this morning by briefly grazing the positive terminal with the negative charging lead. A split-second of sparks ensued and jolted me out of my morning stupor. Is my battery finished or can a SLA battery tolerate this bonehead mistake? :ohgeez:

 

[dannstrait]

When you charge up the faulty battery, only five cells are working and the sixth might be seen as a resistor ... If you put a load on the charged faulty battery, you may well see a voltage drop if only five cells are active ... If you have a Voltmeter, you should be able to check this ... A 12 volt 6 Watt bulb on a couple of lengths of wire will be OK for a load and will take about half an amp drain ... Put your meter across the battery to check the on-load voltage.

I would consider replacing the dropped battery ... Our batteries floated at between 2.24 volts and 2.26 volts, so the initial 12 volt battery voltage after a charge should be about 13.5 volts then it would drop to a lower level ... It shouldn't sink below the 12 volt point though.

Well, I was charging my SLA specifically because I had noticed very poor performance the last few times I used it (before the shorting accident). After reading this thread, I finally understood. I got home from work today and tested the open voltage (12.85 V). This was obviously a bit low for a freshly charged battery. I put a 6 watt load on the battery and watched the voltage depress down to around 11.34 V and falling. I now don't feel so bad about the shorting accident. The battery was finished anyway.

 

[march.brown]

Well, I was charging my SLA specifically because I had noticed very poor performance the last few times I used it (before the shorting accident). After reading this thread, I finally understood. I got home from work today and tested the open voltage (12.85 V). This was obviously a bit low for a freshly charged battery. I put a 6 watt load on the battery and watched the voltage depress down to around 11.34 V and falling. I now don't feel so bad about the shorting accident. The battery was finished anyway.

.
We used to do discharge tests based on a ten hour rate ... The 48 Volt batteries ran all the telecomms equipment on site and the battery capacities were chosen to provide power for at least ten hours ... If the mains or charger failed, we had ten hours to get it all working again.

If you have the time to spare, you can try the discharge test at the ten hour rate ... If you are using a five ampere-hour battery, it is just a matter of putting a resistor of the right value and wattage across the battery and then monitor the voltage reducing as the battery discharges ... It would be an advantage to have a "control" battery which ideally would be a brand new, freshly charged one ... Do the discharge test on the new battery and keep a note of the times and voltages over the discharge period ... We did hourly checks till towards the end when we used half hourly checks ... We had the advantage that our batteries were individual cells which could be replaced as necessary ... Compare the suspect battery results to the good one ... Be prepared to throw out the old one though.
.

 

[march.brown]

.
We used to do discharge tests based on a ten hour rate ... The 48 Volt batteries ran all the telecomms equipment on site and the battery capacities were chosen to provide power for at least ten hours ... If the mains or charger failed, we had ten hours to get it all working again.

If you have the time to spare, you can try the discharge test at the ten hour rate ... If you are using a five ampere-hour battery, it is just a matter of putting a resistor of the right value and wattage across the battery and then monitor the voltage reducing as the battery discharges ... It would be an advantage to have a "control" battery which ideally would be a brand new, freshly charged one ... Do the discharge test on the new battery and keep a note of the times and voltages over the discharge period ... We did hourly checks till towards the end when we used half hourly checks ... We had the advantage that our batteries were individual cells which could be replaced as necessary ... Compare the suspect battery results to the good one ... Be prepared to throw out the old one though.
.

.
http://www.batterystuff.com/tutorial_battery.html You might find this useful.
.

 

[Ready]

Since we are talking SLA batteries...how do you all recommend charging them? I have 2 7ah 12v SLA batteries that I need to keep charged.

I have seen this and wondered if it was a good deal and or the right product:

http://www.batterymart.com/p-12v-1a-sealed-lead-acid-battery-charger.html

Thanks.

 

[march.brown]

Since we are talking SLA batteries...how do you all recommend charging them? I have 2 7ah 12v SLA batteries that I need to keep charged.

I have seen this and wondered if it was a good deal and or the right product:

http://www.batterymart.com/p-12v-1a-sealed-lead-acid-battery-charger.html

Thanks.

.
It has been a long time since I have had to use a charger on 6 or 12 volt Lead-Acid batteries ... My charger is a cheap one and was only used to charge my motorcycle batteries occasionally over winter.

The one that you are asking about has some good reviews by other purchasers ... Can't see anything wrong with it ... It has LEDs to tell you when it is on charge and when the charging has finished ... If you have a cheap DMM then personally I would go for it ... After all, it isn't like charging Li-Ions where the chargers do have to be very accurate.

It is possible that you might get one cheaper, but that one is small and neat ... It will charge at one amp which is OK for small capacity cells, but if you are going to have larger capacity batteries, it would take a long time ... A 7 ampere-hour battery would charge overnight ... If that charger does not cut off when the "Charged" LED comes on, just check that the output voltage is between 2.24 and 2.26 volts per cell ... The float voltage should be 13.5 for a 12 volt battery and 6.75 for a 6 volt battery ... The instruction sheet that comes with the charger should give you their recommended figures.

Good Luck with your imminent purchase.
.

 

[csa]

In response to your earlier question, yes, lithium cells are generally a bit more resilient to things like drops. They're less heavy for the same energy density, and depending on pack makeup, are easier to repair if you do cause physical damage to the cell interconnects.

On the flip side, they're a LOT more expensive.

 

[poguy]

In response to your earlier question, yes, lithium cells are generally a bit more resilient to things like drops. They're less heavy for the same energy density, and depending on pack makeup, are easier to repair if you do cause physical damage to the cell interconnects.

On the flip side, they're a LOT more expensive.

DX has some cheap R/C airplane lithium packs. Looks worth a try. They will be a lot lighter than that big SLA.

NiCad/NiMh packs seem rugged, too. I use them in R/C cars and they take a beating, physically and electrically.

 

[timberwolf]

In general all current high capacity cylindrical cells are quite fragile.
If you drop them and they get dented it will most certainly kill the cell by shorting it out.
Flat lithium polymer may tolerate a drop because of lower weight, but if you apply enough pressure you will se the are quite fragile to.
The problem ist mostly mechanical deformation, not the shock itself.