Simple battery charging question..

[plainman007]

Dear Audioguru,

But how can a normal layman who doesnt have an electronics background understand all this. Its so technical. Im mainly interested in maintaining my batteries properly but dont have much tech knowledge. The radios which i have have no markings on the battery giving the company details etc. I think thats impractical and its very unlikely that all radios batteries carry the address and details of the battery manufacturer. This said, it mentions its a li-poly battery and it also says OUTPUT - 7.4v 1200mah. Based on this can you tell me how this battery should be charged. The chargers that come with the radios are desktop base chargers. The manual says the batts take about 5 hrs to charge and its better to leave it for 2 hrs after the green led (fully charged) lights up on the charger. This has proved right in actual experience. For a fully discharged radio in about 4.5 hrs the green led lights. And we leave it for 2 hrs more and then remove the batt. The dealer said the batt is capable of 450 cycles.

Also after the batt is charged and im not going to be using the radios for say a month. Is it ok to leave the battery with the radio or should i detach the batts. And if the radio is just going to be stored for longer say 3 to 4 months of disuse. Is it good to discharge and the recharge the batt fully once in a month. Is this good for the battery ?

Thanks a lot. I really appreciate your effort in explaining this to me.

 

[Audioguru]

A rechargeable lithium cell has a nominal voltage of 3.7V so two in series are 7.4V. The radio should have a circuit to disconnect the battery when its voltage drops to 6V. The charger should have a circuit to limit the charging current to about 400mA and limit the voltage to 8.4V and disconnect the charging when the charging current drops to about 36mA.

I don't know if your radio has a clock or something that drains the battery when the radio is turned off. It it doesn't then a fully charged battery can sit in the radio for years.

It wastes the limited number of charge cycles to discharge the battery for no reason.

 

[plainman007]

Hi,

I have categorised my questions into basic categories of doubt. Would be great if you can just answer quoting the point no. This will ensure i get all my answers for each doubt that i have.



1. It doesnt have a clock or any function on it. It a very simple type of professional radio. No display nothing. Just on/of & volume on one knob and channel selection on another. I think the radio senses a drop in voltage and then the transmitting LED blinks non stop to show a low battery. I think its safe to off the radio immediately and then recharge as soon as possible right ? Since i think its not good to leave a battery in discharged condition for long ?

2. I dont think it has any function that runs in the background while the knob is in off position. So i assume its ok to just leave the battery packs in the radio ? Cause its so inconvenient and risks ending up with a loose batt clip etc if i needlessly detach the battery every week and put them back in, and that would mean picking up a new radio if the batt clip breaks or something. So is it ok to leave the batt inside ?

3. We use these radios on an average of once in 2 weeks for events. Do you think that kind of usage is enough to keep the battery healthy ? So i can skip the monthly discharge > recharge cycles.

4. If im going to leave the radio unused for about 2 months or so Ill fully charge then discharge to 50% and store it ? I think 50% charge is suggested for storing batteries for long periods ?

5. What is the rough expected life of a battery like this considering our sparse usage pattern ? I mean if a person charges & uses this radio once in 3 days and gets x years of life span out of the battery. If a person charges & uses it 3 times in a month will he get a longer life of battery or is the life span duration fixed irrespective of charging pattern.


Thanks a lot for your contributions. I think this post will turn into a mini course on battery maintenance for all people who seek advice on this particular subject.

 

[Audioguru]

1) An electronic device that is powered by a rechargeable lithium battery is supposed to detect a low battery voltage (about 3V per cell) and switch off the load.
2) Yes leave the unused battery in the radio.
3) Yes do not discharge/recharge that wastes cycles.
4) A 40% charge is recommended for storage for years but you cannot determine 40%. For only a couple of months then leave the battery fully charged.
5) The battery can be charged/recharged about 450 times if it is not overcharged and if it is not discharged below 3V per cell.
Read about lithium batteries at The Battery University on the web. There are many other Battery Maintenance sites on the web.

 

[plainman007]

Hi Guru,

Thanks a lot for your help. I only didnt understand answer 1. My question was when the radio beeps a low battery alert. It must be switched off and charged asap ? Or a drained battery can be left for a few days before recharging without damage to the battery ?

Thanks

 

[Audioguru]

I don't know if your radio is smart enough to switch itself off when its battery is low.

I think you should charge a drained battery immediatyely because if you don't then it might be left discharged for too long.

 

[plainman007]

Hi Audioguru,

So I think im safe with just using these radios and not bothering about battery conditioning etc since im going to use them approximately once a week or at least 3 times a month. If im not going to, maybe during the vacation months, then i will fully charge them and shelve them till next use which anyway wont last more than 2 months at a stretch.

What kind of batteries do UPS units and Emergency lights mostly use ? Lead acid ? Or are they also mostly sealed gelled batteries ? Do emergency lights which get used only once in a bluemoon need to be conditoned once in a while ?

Thanks...

 

[Audioguru]

Correct.
You do not need to condition a lithium battery.

Correct.
UPS units and emergency lights use lead-acid batteries. Their charger trickle-charges them all the time to make up for self-discharge and maybe they are quickly tested once in a bluemoon.

 

[plainman007]

But what if an emergency light isnt always plugged into the wall socket. I mean its fully charged but then stowed away for emergency use. Then used ocassionally (twice a month) for maybe 30 mins.

Is this kind of usage ok ? Or does this usage pattern of Lead Acid Batteries qualify for battery conditioning (full discharge and recharge) maybe once in a month or on a quarterly basis.

Thanks.

 

[Audioguru]

A lead-acid battery should always be fully charged. After sitting for a few months it gets sulphated and is ruined.
If it is used then it should be charged immediately.
It should be trickle-charged to make up for self-discharge.

There is no reason to wastefully discharge a lead-acid battery.

 

[plainman007]

Hi,

1. What if its not sitting for months at end. Maybe Just a month or 2 and then fully charged.

2. From what i understand about what you said. I think its better not to discharge the battery but better to just top it up once in a month ? If so how do i know how long to leave it in...just leave it overnight ? cause if its a trickle charge unit it wont overcharge right ?

3. Of course if this is connected to power always then i guess its being trickle charged internally in the light unit.

Thanks..

 

[Audioguru]

You should use a proper battery charger circuit. It will not over-charge your battery but a cheap charger will.

A proper battery charger circuit will trickle charge your lead-acid battery all the time after charging it.

 

[bikashh]

will there be any problem if i keep the battery connected to the charging circuit even if it is full.

 

[Audioguru]

will there be any problem if i keep the battery connected to the charging circuit even if it is full.

A lead-acid battery goes dead and is ruined in a few months if it is not trickle-charged or periodically charged. The voltage of the trickle charge must not be more than 13.8V or the battery will dry out.