Amperage as it applies to Batteries

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MM7

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Jan 2, 2010
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Boy am I hoping some one can straighten me out on this.
I am working with SLA batteries but this should be applicable to all types (I believe)
The question is this: If a 12V 7AH battery's amperage drops to 4.5 amps; what exactly is this indicating? I have a friend who services alarm panels and uses 12Volt 7AH SLA batteries as a built in back-up. He tells me the alarm panels internal testing system monitors the amperage of the batteries and when the amperage drops below 4.5 amps he is required to change them out for new batteries....I offered to take them off of his hands rotfl to use on my e-bike projects. I just have not quite figured out if these batteries are still worth the effort. My brain is saying 7AH down to 4.5A means I have 64% of the battery still to use up. {they are rechargable so there should still be over half the charge/discharge cycles left in the battery; so to speak}.
If this has made any sense at all could someone out there smarter than I am let me know how far off the mark I am?

Thanks a Lot,
Matt
 
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2door

2door

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Sep 15, 2008
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Your friend is right about the batteries requiring replacement when they test bad. Local fire departments as well as the NFP (National Fire Protection) codes also dictates how often panel backup batteries are replaced. He probably uses a tester to load the battery and depending on the readings he gets, either replaces it or leaves it for next time. Most fire alarm panels self test and will put the panle in a 'trouble' mode if the batteries are bad.

SLA, (sealed lead acid) batteries are just like the one in your car. They can test good as far as voltage goes when unloaded but due to a defective cell, bad plates or internal shorts, will not be able to carry the amperage load required. If they tested bad in the panel then they probably won't power your bike.
Tom
 
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MM7

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Jan 2, 2010
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2-Door,
Thanks for the reply but i am still a little in the dark as to whether a SLA 7AH battery that tests out at 4.5amps is any good and how much is left in the battery. You mentioned that the battery is tested "under load" to get the amperage reading. Could you describe how this test is done so that I could reproduce it?
Sounds like an important skill to have if ya do any work at all with battery powered bikes.:confused: Plus I really like the idea of recycling the rechargeable batteries he is changing out. My buddy admitted that the batteries are no where near used up (in his opinion).
I really want to get my head wrapped around these concepts but I'm finding straight-forward information on batteries a little difficult to come by.

Thanks Again 2-Door.....anybody else have 2 cents to add????

Matt
 
2door

2door

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Staff member
Sep 15, 2008
16,302
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Littleton, Colorado
MM7,
By 'loading' I mean introducing a load on the battery instead of just checking the voltage with a meter.
Example: attach the leads of a large wattage light bulb or a motor, of the same voltage naturally, at the same time put the test leads of your meter on the battery posts. Check the voltage before attaching the load then while the load is attached.
A good battery will show a slight drop in output voltage with the load connected but a bad battery will show a dramatic decrease in meter reading.
Your friend probably uses one of the newer generation of solid state testers, which being the dinosaur that I am, never trusted. I like to see a real worl load placed on the battery such as a lamp or motor, even a resistance heater. Hope this explains it for you.
There is a lot of good information on the Internet about batteries and checking them and with a little research I think you'll find all you need to know
Start here> http://www.power-sonic.com/index.php
Tom
 
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motorbiker

New Member
Mar 22, 2008
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Tampa Bay Florida
MM7 said:
2-Door,
Thanks for the reply but i am still a little in the dark as to whether a SLA 7AH battery that tests out at 4.5amps is any good and how much is left in the battery. You mentioned that the battery is tested "under load" to get the amperage reading. Could you describe how this test is done so that I could reproduce it?
Sounds like an important skill to have if ya do any work at all with battery powered bikes.:confused: Plus I really like the idea of recycling the rechargeable batteries he is changing out. My buddy admitted that the batteries are no where near used up (in his opinion).
I really want to get my head wrapped around these concepts but I'm finding straight-forward information on batteries a little difficult to come by.

Thanks Again 2-Door.....anybody else have 2 cents to add????

Matt
Click to expand...
Read Deacon's posts. He likes testing out different stuff.

I think he would say try them and see how far they will push you . :)

A basket or baskets on the back gives room to hold different batteries for testing.
 
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Erich_870

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Dec 4, 2009
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Alaska
I wonder if you can get a battery charger with a reconditioning feature and bring them back to life, even if just back to 75-80%.

[Edit] I did a quick search and this did not apply to SLA batteries, so I've removed it. It has to do with NiCad batteries.

I'd take those batteries to play with if he was my buddy :)

Erich
 
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2door

2door

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Sep 15, 2008
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Littleton, Colorado
Erich_870 said:
I wonder if you can get a battery charger with a reconditioning feature and bring them back to life, even if just back to 75-80%.

I've read of guys trying to bring their cordless drill batteries back by using a mig welder and striking the contacts a couple of times. Supposedly it breaks down the internal pathways that cause a battery to not hold a charge. They used plenty of PPE (personal protection equipment) when they used the welder :)

I'd take those batteries to play with if he was my buddy :)

Erich
Click to expand...
This is a very dangerous suggestion. Personal Protection Equipment aside, you're talking about a potential bomb. Can you say hydrogen explosion? I've never heard this theory but strongly place it in the catagory of using a cigarette lighter to see how much gasoline is left in my tank.
My advice? If the battery is dead properly dispose of it and buy a new one. Do not try the suggestion given here.
Tom
 
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Erich_870

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Dec 4, 2009
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Alaska
2door said:
This is a very dang
​
erous suggestion. Personal Protection Equipment aside, you're talking about a potential bomb. Can you say hydrogen explosion? I've never heard this theory but strongly place it in the catagory of using a cigarette lighter to see how much gasoline is left in my tank.
My advice? If the battery is dead properly dispose of it and buy a new one. Do not try the suggestion given here.
Tom
Click to expand...
[Edit] I've edited my post above.

Erich
 
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MM7

New Member
Jan 2, 2010
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Texas
Guys,

Thanks a lot for the different suggestions generated by my questions. I think I can use the information here to get me pointed in the right direction now.
Again, Thanks Everyone!

Matt
 
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