Recharge When?

[ArcticDiver]

When and how often to recharge batteries is a recurring question with answers that change over time. What I've been reading says there are two key factors: Charge/discharge cycle and Capacity.

Each battery has only so many charge/discharge cycles before it in effect wears out. To use the cycles most efficiently it is best to let a battery become as fully discharged as practical before recharging. "Topping off" wastes cycles and wastes battery capacity.

So, the best practice is to use a battery as long as possible before recharging.

Opinions?

[Jeff Pack]

depends on the battery type.

NiMh you keep full charged, prob charge once a month, or every 2w for the anal retentive.

Lithium you store anywhere from 70-90% of full charge. Some folks actually store lithiums in the freezer I think. Or was it frig, I dont remember. I dont do this myself, I just recall some folks doing so in the RC world.

I've got a Hyperion charger/discharger I use, as it supports charge, discharge, and store modes across diferent cell types, plus has a computer interface to graph discharge curves and log cell data.

[Dusty2]

Those are OLD facts that applied to NiCD batteries. If you are using NiMH or Li-ion the rules change drastically. Unlike the newer batteries NiCD's do have a finite number of cycles and should be cycled only when they are well drained.

The newer batteries do not have this problem. If properly cared for they will last indefinitely. NiMH batteries should be charged before they reach 40% of capacity to avoid damage to the batteries. My policy is charge after every use. It does no harm and your bats will stay nice and healthy. Another thing to remember is that all bats loose power over time. If you are going to store them for an extended time make sure they are fully charged when stored and they should be cycled every 3 to 6 months to insure they don't drop below the critical point. This for battery packs. Individual batteries are not so fussy.

[lamont]

deep discharging batteries is significantly worse than lots of top off charges, you should be more worried about discharging than number of cycles.

when storing nickel batteries they'll self-discharge faster than other chemistries and will need to be recharged more often to avoid deep discharging them while stored.

[CaptnJack]

Those "rules" don't apply to any battery chemistry.

There's no faster way to kill any kind of lead acid (wet, sealed, or gel) battery than through deep discharges. Cycling between 50 and 100% of charge and they can last thousands of cycles. A few complete discharges (<20% of charge) and they will be permanently reduced in capacity.

[ArcticDiver]

Interesting. For further discussion:

-Duracell specifically says to store their batteries in a cool, dry environment. Refrigeration or freezing will not lengthen battery storage life and may shorten it.

-Instructions with a device I recently purchased that has rechargeable lithium(specific chemistry unknown) says to only recharge when there is no useable capacity remaining. Device circuitry will turn off the device before battery voltage becomes too low. The instructions with the device says that the batteries have approximately 500 cycles before needing to be replaced.

-There are "deep discharge/cycle" batteries that are speifically designed for that purpose. These are often used in marine, golf cart and PV applications. Doubt they are in many scuba specific applications/devices.

[oldsalt]

This sounds like the old Jewish saying, "You ask three rabbis a question and you get four opinions." I know that my AGM (absorbed gas membrane) house batteries on Windwalker came with about 20 pages of operating instructions. I had to reprogram the alternator and battery charger to conform with the specs, which gave different settings depending on the average temperatures expected. I ended up calling tech assist several times to get the guy who knows. He said, "It really doesn't matter that much." Going online for more info overwhelmed me with the variations among AGM's. These are expensive batteries. I have been told it was the dumbest thing I've ever done (Not even close.) and that it was the best investment I could make. These are advertised as deep cycle batteries, and I run them down. The alternator and charger are supposed to take care of them. So far so good. If one day I plug in the coffee or punch the button on the microwave and nothing happens, then I'll know. O yeah, I studied electrical engineering, and I still don't know.
-Curt

[airsix]

You know what a deep-cycle lead acid battery is? It's just a very high amp battery that they know is going to be abused. There is nothing special about it. This was confirmed in a conversation with a chemist that works for Interstate. It suffers just as much from deep discharge as a standard battery. They just build it with extra capacity so it takes longer to destroy it.

Deep cycling lithium rechargeables is damaging. Period. Storing them at full charge is also not best, but it's better than discharged. I try to keep mine stored between 40-80% charge, and top off right before planned use.

[Jeff Pack]

Typically a Deep Cycle just has thicker plates, and sometimes the plates are slightly higher off the cases bottom, to allow more crap to build up before shorting the plate.

[fmerkel]

Here's a pretty good reference on battery technology. It's more accurate than most of the stuff you find on the internet, especially forums.

http://batteryuniversity.com/learn/

FWIW, I charge my NiMh after use and just top before use if they've been sitting awhile. The older, more abused, and lower grade will self discharge faster.

I keep my infrequently used lithium polymer (RC) at ~ 40-70% charge and in Zip-locs in the fridge. Warm and charge just before use.
Lithium ion (most likely chemistry used in Scuba) is more robust. If used a lot I'd put it at the 40-70% level after use and top just before use. I wouldn't bother with the fridge. I would not charge right after use if going to be sitting until next weekend.

Lithium is damaged by over discharge and degrades if stored at full charge, especially at higher temps (hot garage, super hot summer car, etc.)

All rechargeable PACKS will suffer negative consequences from over discharge. Some 'may' recover better than others but the damage mounts up. Some never recover.

Yes, you'll need a better grade of charger for some to storage (40-70%) charge.

[ArcticDiver]

It is interesting the different responses. Like oldsalt I have discovered that different "professionals" give different answers on the same subject. I posted here because although I'm pretty conversant with battery technology, having designed and installed many remote PV systems and operated and maintained marine and aircraft systems, I 'm not that up to speed on scuba applications.

The basic chemistry and components of all batteries are similar. What makes them specific is how that chemistry and component selection is used in their construction. Some are built to be able to tolerate brief, heavy current draws, others just to loaf along. Some will take a lot of physical punishment while others are relatively delicate. All batteries have finite lives just from being used. The discharge/recharge cycle never takes the battery back to where it started so it is inevitable the battery will fail at some point. One of the main points of battery design is to construct the battery so it is appropriate for the job.

What is interesting though is that I've yet to find a manufacturer who advocates storing batteries in a refrigerator or freezer. Yet, that seems to be a common tactic used by some users. On the other hand all caution against excess heat. In PV systems it is common to put a sensor on the battery to shut off charging when the battery gets too hot; mainly from heavy charging.

A uniform recommendation seems to be to keep all cells/batteries in a pack/system the same and to not allow the pack/system to become too discharged. That has more to do with the characteristics of the pack/system than an individual battery.

One thing all agree on is that batteries look very simple but in reality aren't.

[Johnbhutch]

Here's a pretty good reference on battery technology. It's more accurate than most of the stuff you find on the internet, especially forums.

http://batteryuniversity.com/learn/

FWIW, I charge my NiMh after use and just top before use if they've been sitting awhile. The older, more abused, and lower grade will self discharge faster.

I keep my infrequently used lithium polymer (RC) at ~ 40-70% charge and in Zip-locs in the fridge. Warm and charge just before use.
Lithium ion (most likely chemistry used in Scuba) is more robust. If used a lot I'd put it at the 40-70% level after use and top just before use. I wouldn't bother with the fridge. I would not charge right after use if going to be sitting until next weekend.

Lithium is damaged by over discharge and degrades if stored at full charge, especially at higher temps (hot garage, super hot summer car, etc.)

All rechargeable PACKS will suffer negative consequences from over discharge. Some 'may' recover better than others but the damage mounts up. Some never recover.

Yes, you'll need a better grade of charger for some to storage (40-70%) charge.

Hark real information rather then 50 different opinions? Are you sure you can not get in trouble for this?

[ArcticDiver]

I asked Duracell for the authoritative answer on when to recharge their batteries. I figured they would be typical. They say to use their rechargeable batteries until they no longer have enough energy to do the job before recharging. The answer also said a user should get about a hundred cycles from their batteries.

Previously their info said for best life to store batteries in a cool dry place and not to refrigerate.

Guess that should answer questions unless there is something scuba specific they don't know.

[airsix]

What battery type are you talking about? There is no single method that is universally optimal for all battery chemistry types. Duracell's advice might work fine for NiMH, but would be abusive to lithiums.

[Gdog]

Actually, deep cycle batteries contain a higher content of antimony, with thicker plates and denser paste, with thicker separater envelopes. They can handle fuller deeper cycling than the regular lead acid battery as a result. They tipically have less cranking amps as well.
Also, Interstate batteries are manufactured by a company called Johnson Control. This company not only manufactures Interstate, but a number of other brands. The only difference at all between an Interstate battery and the rest is that Interstate uses virgin material in its case, where all the rest use recycled material. Hence the reason for Interstate's white opaque case, and everyone elses black case. I have watched on several occasions the entire construction process, from the formation of the plates from spools of lead, the foundries, the packing of the plate material, ect. At the end of the line, in the acid filling, there is a line containing Interstate, Diehard, Duralast, ect. in fact most of the name brands. Not included are Exide, Delco.
Reminds me of the time when as a young man I worked in the sugar beet factory in southern Idaho. I worked bagging sugar. On any given day, we would bag x number of bags of White Satin, the premium stuff, x bags of western family, x bags of generic, x bags of "put your favorite brand here". The crazy part was, it was all the same suger, pouring out of the silos into the bags we sewed shut and palletized.
Ok...sorry about the hijack. Had to interject my 2 bits. Now back to the regularly scheduled show.....

[Gdog]

and wow...please forgive my poor spelling in the previous post....maybe a bit too much scotch tonite?
Please feel free to totally disregard both of these posts...lol

[lamont]

Guess that should answer questions unless there is something scuba specific they don't know.

call them back up and ask them about running them to power a heating vest for scuba diving that is entirely analog 'circuitry' and has absolutely no low voltage cutout and ask how careful you should be of deep discharging them, and make you specify that the battery chemistry is lithium. make sure you're talking to someone that knows something about their batteries and not a sales/PR person reading from a script.

[Dashrynn]

Guess that should answer questions unless there is something scuba specific they don't know.

call them back up and ask them about running them to power a heating vest for scuba diving that is entirely analog 'circuitry' and has absolutely no low voltage cutout and ask how careful you should be of deep discharging them, and make you specify that the battery chemistry is lithium. make sure you're talking to someone that knows something about their batteries and not a sales/PR person reading from a script.

Traditionally batteries haven't used protective circuitry (unless you count fuses or breakers etc etc). Lithium safety requirements change the usual build though, now with lithium ion, we need protective circuitry somewhere. A smart and safe battery pack builder knows to install a PCB to control output/input. If they don't, they shouldn't be building them.

All Lithium battery packs I've torn into or built myself have a pcb to protect them from low and high voltage. Though I have conducted tests on the cells I buy and concluded it takes a severe overcharge to make the cells go boom (for the other test I tied the wires together and watched it closely, no explosion). Battery accepted a charge after 0 voltage draining, no telling what damage I had done to it though until further testing.

[airsix]

Lithium low-voltage cutoff circuits prevent destroying cells, but deep discharges that never reach the cutoff voltage still shorten service life.

As Lamont implies, I'd expect anyone you talk to at a Duracel 800 number is going to give you info for consumer-grade primaries (i.e., single-use alkalines) or their NiMH rechargables they sell in grocery stores. I don't think the 1st level support binder has a section for balanced multi-cell lithium packs required to provide 10 amps at a 100% duty cycle.

[ArcticDiver]

From the posts to this thread even the most uninterested should get the idea that batteries are actually complicated things. Also, that there are limits to intelligent conversations in a medium such as this. Over the years I've discovered in the PV, Marine and Heavy Duty worlds there are a good number of people who are heavily invested in their opinions even though they are either wrong, or don't really make a difference.

It really is a red herring to make comments about different batteries without acknowledging that batteries are generally built for specific purposes. The internal construction of batteries built for different purposes will be significantly different. A battery built for deep cycle, heavy load or extreme temperatures will generally be different than one intended for minimum weight in the family sedan. At the same time best results are obtained from proper battery selection.

My Duracell conversation is with their engineers. My original email specifically asked for them to specify any differences between how chemistries are treated. Their reply did not mention any differences. But, like airsix, I think, in fact, there are. So, I've asked again. Let you know what they say.

[airsix]

Here's a tidbit about Lithium deep discharges. The Nissan Leaf EV apparently has a software controlled low-voltage cutoff that is quite high. Now why would they intentionally program a cutoff voltage that shortens the vehicle's range? Wouldn't they want to squeeze every drop of mileage out of a charge they could to promote their product? They did it to extend the service life of the batteries (a lithium variant called Lithium Manganese). By avoiding deep discharges they are hoping to have fewer warranty claims (8yrs or 100k miles). Some users are hacking their Leafs to lower the cutoff voltage in order to extend range, but at the expense of service life.

[ArcticDiver]

Interesting item was the instructions for one of my recently purchased devices. It has Li, don't know exactly which chemistry, batteries. Instructions(paraphrase obviously) say to try to use as much of each battery charge as you can before recharging to get most use from the limited recharge cycles. Actually that makes a lot of sense if there are limited charge/discharge cycles and there is protective cirucuitry.

Until airsix's comments I didn't realize there were any usual applications where there was not some kind of low battery protection circuitry involved. So, taking precautions to not over discharge a battery were not in the vocabulary. So, when I commented about discharging as far as possible I never considered someone might deliberately defeat the protective circuits. In my mind they have a low regard for their personal safety.

[CaptnJack]

I asked Duracell for the authoritative answer on when to recharge their batteries. I figured they would be typical. They say to use their rechargeable batteries until they no longer have enough energy to do the job before recharging. The answer also said a user should get about a hundred cycles from their batteries.

Wow they know how to sell batteries don't they?
If you keep NiMH at 50% duty cycle you'll get 500-1000 cycles out of most consumer brands. 100 cycles is an absolute joke.

Would you have 100x 100% duty cycles or ~750x 50% duty cycles? Which is the better value?

[airsix]

Arctic, piggybacking on Richard's last post...
Charging from 50% is not the same as charging from a fully-discharged state in tems of "using up" charge cycles. In fact charging from 50% "uses up" less than half of the service life that a full discharge/charge does. So if you only discharge to 50% you should in theory get MORE than twice the charge cycles than if you fully discharge.

[ArcticDiver]

I'm not sure what their claim of available duty cycles has to do with sales; except that it would discourage me from buying their batteries. I assume these batteries are no different than those I'm accustomed to using. For those the rule is to use until failure unless in certain critical applications then to determine life in that application and schedule replacement before failure.

You two seem to be "Battery Authorities". From whence comes your expertise?