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Simple battery charging question..

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Dear Paul,

You said "If you want to measure the battery capacity, discharge it using a constant load (like a bulb or a resistor) and measure the time for the output voltage to drop to about 12V."

Can you kindly explain what you mean by that. I understand discharge it using a constant load. But what do you mean by measure its capacity please ? Does that mean measure how much the battery is CAPABLE of handling. Or how much charge it CURRENTLY contains ?

Sorry im asking so many questions for such a simple concept as i dont know much about this.
 

Means you are going to measure the actual amount of charge the battery contains. As noted above, you need to use a light load. I suggest your using a 330Ω / 1W resistor to discharge it for about 20h if it is fully charged.
 

Dear Paul,

I have absolutely no experience in electronics and capacitors and resistors etc. Im just a layman who happens to work with some electronics in my work and needed advise towards some of my work related stuff.

I can however understand discharging the battery using a 12v bilb etc as thats more on a mundane level.

I think in order for me to understand the way the charge works is to let you know that ive charged the battery which i had on the shelf unsed for about 8 months or more. So i connected it to a charger which is like a cellphone plug in charger and has a label on stating 220V. It was provided by the guy who designed the motor display thing for an exhibition and this is the battery is to be used in that gadget, but very occasionally. Now after 8 months of storage i charged the battery using this charger for about 20 hrs. Then i measured it the next day using a mutlimeter and it displays 12.2 or something. Whats does this mean at the moment, it contains a full charge ? or just that its giving out 12v ?

Thanks
 

If you left the battery on the shelf for 8 months or more chances are that some sulfatation happened to the battery´s plates because it was fully discharged. In other words, maybe it has no longer the full capacity as when it was new. When it is fully charged the voltage reaches about 14 to 14,5V with a very small current needed to keep this point (called the floating point). After reaching the floating point, if you turn off the charger, the voltage rapidlly decays to 13,6 to 13,2V (in a few minutes) and then goes slowly to about 12,6V with no load. Voltages may differ somewhat depending on the battery type and manufacturer. If you are reading 12,2V it is probably not fully charged OR you are experiencing the effects of a damaged or long time used battery. My suggestion is:
1- Keep it charging for more time and see if it reaches the floating point (just measure the voltage with the charger connected)
2- If the voltage keeps within the expected floating value, leave it charging for more time (1 or 2 days). Usually those batteries recover part of the damage by sulfatation (not all).
3- Apart from the fully charged and fully discharged voltages, any other voltages you read can´t tell you anything about the amount of charge of the battery.
 
Hi,

Sorry to return to this thread late.

So the multimeter can only tell me what voltage is coming out. Not how much of the charge is in the battery or if its draining to fast ? (lost its capacity).

This battery is meant to drive a small motor of 12v DC with heavy torque. Is the best layman way to identify gow the making an automobile 12v battery and connecting it to this battery. If the battery is good it should burn bright and long ? Or at least i will know how long the battery will supply a 12v power ?

Please do let me know. Thanks for your immense patience trying to explain this to me.
 

You destroyed the battery by leaving it sitting for months without a charge.

It is lead-acid like a car battery that is supposed to be charged almost every day.

I have a Lithium battery from my daughter's first cell phone that is about 12 years old and it is still charged. It was last charged about 11 years ago.
 

Agree, your battery is dead. The lead acid gel batteries are especially delicate because the electrolyte is not a liquid. Damage to the plates by sulfuration is not reversible and rapid charging will cause gas to form between the plate and the gel electrolyte which then makes them lose contact (usually permanently) Never let one of these batteries go below 50% discharge to keep them long living. I know I have ruined my fair share of them.
 

I dont know if my battery is the lead acid type. Its like a hard plasticine thing. Fully sealed. And just two metal plate terminals peeping out.

Snafflekid > I dont understand how one could never let these batteries go under 50% charge ? First off theres no way of immediately telling how much of the fully charged battery has been used. So how would i determine if its around 50% charge. Ive still not understood how to use the multimeter to find out when the charge is dropping. When a 12v 8mah battery is fully charged how much would it show on a multimeter ? And when the battery is at 50% charge what will the multimeter show then ?

AudioGuru > I have walkie talkies that work on lithium polymer batteries (Li-Poly). Im using the radios on a regular basis so i think that way im safe. Also the radio manual says to wait for the batteries to get fully discharged (the raidos batt low indicator sounds) before recharge. Also it mentions that if not in use for around 2 months or so that we should completely charge and discharge several times to regain the batteries full capacity. Whats your take on these batteries ? If i dont plan on using them for a long while, should i just completely discharge and reacharge the battery maybe once in a month to keepgood battery life ?

Thanks
 

A car battery is a lead-acid type and it never sits for months without a charge and it is never discharged below about 80% of a full charge. Then it lasts for about 5 years.

Your little 12V/8Ah battery must never sit for months without a charge and must never be discharged below 50% of a full charge.

You can measure its voltage when it is charging (and not loaded) and it will be 14.0V to 14.5V when still charging but fully charged. If you let it sit for 10 minutes without a load then its voltage will drop to 13.2V to 13.6V. In two days the unloaded voltage will drop to 12.6V. When the unloaded voltage drops to 12.2V then it should be charged.

A lithium battery cell is 4.2V when fully charged and the 4.2V charging voltage must remain until the charging current drops to a few percent of its capacity. A circuit must disconnect the load when the voltage drops to 3V. I think your radios have the low voltage disconnect circuit and then the charger is probably simply a timer that assumes the battery is discharged to 3V.

A lithium battery cell holds its charge for years if it has no load. Maybe your radios have a clock or something that slowly discharges the batteries.
It does not need to be discharged to be recharged unless the charger is simply a timer like yours.

An old Ni-Cad battery loses much of its charge sitting for a couple of months. They were discharged then recharged frequently.
 

Hi,

But the radios say they are li-poly batteries. Ofcourse the radios are extremely light for a pro 2 way radio. Its a lithium polymer battery as the manual mentions. Now if its a lithium battery, why does the manual say if not used for more than 2 months to completely charge and discharge several times to regain their full capacity ?
 

Battery manufacturers do not say that Lithium batteries need to be discharged and recharged.
Also my lithium batteries do not.

I think your radio manufacturer wrongly copied the manual from an earlier radio that used an old Ni-Cad battery.
 

Hmm there cant be a mistake in the manual because they clearly state that its a LI-Poly (which is the actual type of battery in the radio) and that it should be maintained this way for best performance.

I think the best way to keep batteries active is by using them a lot hmmmm :)

But irrespective of which type of battery, its alway better to wait till a battery is almost completely discharged and then recharge it again ? Or do you recommend half consumed batteries being charged as is to full ?

Thanks
 

Your radio manufacturer does not manufacture Li-PO batteries. Look at the website of the battery manufacturer to see about their batteries.

A Lithium battery has only a certain number of charge-discharge cycles before it is dead so wasting some cycles will shorten its life.

Each battery type is different.
A lead-acid and a lithium battery are destroyed if they are discharged too far. A Ni-Cad or Ni-MH battery cell doesn't care if it is discharged to 0V, but then in a battery some cells might become reversed voltage which will destroy them.
 

Just one more thing to clarify. So when a battery is fully charged it attains its voltage (which can be seen in a multimeter) as 12v if its 12v battery or it usually is supposed to show more. Then as it is used it keeps on supplying 12v dc and at anytime that its considered delivering power ? the mutimeter would show 12v or more only ? And then as a batt requires to be charged it drops and shows lower readings on the multimeter.

Ok let me ask it in a more simple way. I charge a 12v dc battery fully. I test it with the MM. Its shows 13v maybe. Then i start using it. After a few usage sessions it shows 12v on the MM. Then some more usage and it shows 11 or maybe 10v. Is it time to charge it ? At which stage would you say the battery has depleted and needs a charge ?
 

Each cell of a lithium battery is charged to 4.2V.
So 3 cells in series charge to 12.6V. The minimum allowed voltage for a lithium cell is 3V so when the battery voltage drops to 9V then the load should be disconnected and the battery should be charged properly.
 

But how do i know how many cells are in my battery. It looks like one plastic square block. With everything sealed and is supposed to be maintenance free. It has just two small terminal plates emanating from within the battery.
 

plainman007 said:
But how do i know how many cells are in my battery. It looks like one plastic square block. With everything sealed and is supposed to be maintenance free. It has just two small terminal plates emanating from within the battery.
Click to expand...
Are you talking about the Li-Po battery in your radio? Or a sealed gel-cell lead-acid battery?
 

Any battery ? Wether a gel battery or a gel sealed battery ? How does one tell how many cells it consists of ?

Thanks
 

i know the Sealed bateries isstandardized in sizes. Capacity depends on size and since there are many competitors in the market, the same size means the same capacity


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**broken link removed**
 

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