Storing Lithium Batteries

[Buadhai]

I purchased a new dive light earlier this year which came with two lithium batteries. I was pretty careful to alternate the batteries and to store them, charged, in a cool, dry place.

After not diving for a couple of months I was surprised to find that one of the batteries had dropped below the voltage at which the protection circuit was still active and could therefore not be charged in an ordinary charger.

Does this mean that I need to periodically charge the batteries when not in use? If so, how often would be appropriate?

 

[DeepSeaExplorer]

Lithium batteries loose their charge faster than most chemistries. If it were me, I would charge them at least once a month.

 

[Bobby]

That is incorrect. Li-Ion batteries hold their charge the longest. It is not uncommon for me to have batteries sit for 6 months and only loose a small portion of their charge. It is not suggested and not needed to top off Li-Ion batteries like we had to with the old NiMH. If your battery lost that much voltage in two months then you likely had a cell go bad or it was not charged after complete discharge.

If you take it to a battery shop that has a good programmable charger they can run a test to see what the issue is. If it is simply being under the minimum voltage there is a chance that they can run a low voltage recovery cycle charge on it and bring it back. If you have a bad cell I would suggest replacing the entire pack. Li-Ion cells need to be matched so having used cells with one new one is not a good combination.

 

[Buadhai]

Thanks. The torch only takes one cell and that's really all I need.

There's pretty much zero chance of finding a battery shop here in Korat (rural Thailand).

So, you think there's no need to recharge on a regular (monthly) schedule?

 

[MikeRD03]

Every battery pack and even one single cell should have a protective circuit against over- and deep discharge. These circuits eats little current, so a charge to 50% would not be to worst to do after some months.
The Li-Io cells itself have nearly no self discharge.

 

[DeepSeaExplorer]

That is incorrect. Li-Ion batteries hold their charge the longest. It is not uncommon for me to have batteries sit for 6 months and only loose a small portion of their charge. It is not suggested and not needed to top off Li-Ion batteries like we had to with the old NiMH. If your battery lost that much voltage in two months then you likely had a cell go bad or it was not charged after complete discharge.

If you take it to a battery shop that has a good programmable charger they can run a test to see what the issue is. If it is simply being under the minimum voltage there is a chance that they can run a low voltage recovery cycle charge on it and bring it back. If you have a bad cell I would suggest replacing the entire pack. Li-Ion cells need to be matched so having used cells with one new one is not a good combination.

My bad... All I can say it was early. I was thinking NiMH which can discharge as high as about 30% per month vs LiPO which are about 2% to 5%. That said, however, it does depend on the battery manufacturer/quality. When you get Class A batteries vs C or D, you can really tell a difference. LiPOs of lesser quality will discharge much faster than the advertised rate. So, back to my original statement. Charge/monitor them once a month. They're too expensive to not keep an eye on.

 

[Hatul]

I purchased a new dive light earlier this year which came with two lithium batteries. I was pretty careful to alternate the batteries and to store them, charged, in a cool, dry place.

After not diving for a couple of months I was surprised to find that one of the batteries had dropped below the voltage at which the protection circuit was still active and could therefore not be charged in an ordinary charger.

Does this mean that I need to periodically charge the batteries when not in use? If so, how often would be appropriate?

An I ask you what battery this is?

 

[Buadhai]

It's an UltraFire BRC18650 which came with an Archon dive light.

 

[Hatul]

It's an UltraFire BRC18650 which came with an Archon dive light.

I don't know the answer to your question, but the 18650 batteries are really inexpensive. What I'd suggest is an XTAR charger like the VP2, which shows the voltage and the state of charge of the battery so you can see yourself if the battery is self discharging and the rate.

XTAR VP2 Charger | XTAR Direct

 

[Dr. Lecter]

I know the lithium batteries in my can light and DPV are best stored at around 50-60% charge. I would imagine that which flavor of lithium chemistry battery varies that some, but stored with half to 2/3s charge is probably going to be a good rule of thumb.