How to drain a battery

 
Maybe a silly question, but any thoughts on how to effectively drain 12v battery after a day on the water?  I'm considering this in an effort to prolong the life of said batteries.  FISH finder, trolling motor ext.  I've heard it is better to keep a dead battery for long term storage than a partially charged one.  Though best is to have a battery tender hooked up (not practical).  Maybe I'm over thinking it.
Thanks,
J. Ice

You can hook the battery to a lamp or resistor to discharge it.

I am absolutely not an expert, but I thought just the opposite was true, to prolong the life of a battery keep it charged, not so much with  tender but at least charge it periodically.  I've also always believed that once a battery is dead, if you leave it that way for long, it'll be dead for good.

So with that said, I hope to learn something from your post. 

As for drawing it down I'd just wire up a 12v lite to it. Of course that might take awhile.

Like I said, hoping to learn from your post.

A lead acid battery prefers to be stored at a charged state with a tender as you stated.  Lithium batteries need to be stored at 3.8 volts per cell which is in the middle of their charge state to not lose life.

You could just leave your FF on once you get home.
Some chargers wont even turn on if the batt is below a certain voltage. At least on SLA's.

A lead acid battery prefers to be stored at a charged state with a tender as you stated.  Lithium batteries need to be stored at 3.8 volts per cell which is in the middle of their charge state to not lose life.

That. If you leave a LiPo stored at full charge, the battery pack will inflate and shorten the lifespan. All of the equipment in the picture can be used for discharging. Some are more efficient than others. My current favorite is the ISDT FD-100 for lithium batteries.

ernest

Thanks for the reply, all that said, so what's best shared periodically and kept charged or dead? What's the consensus?  If I'm gonna run it down I'll set up a 12v fan and keep the garage breasy
Thanks
Ice

The recommended storage temperature for most batteries is 15°C (59°F); the extreme allowable temperature is –40°C to 50°C (–40°C to 122°F) for most chemistries. While lead acid must always be kept at full charge during storage, nickel- and lithium-based chemistries should be stored at around a 40 percent state-of-charge (SoC). This minimizes age-related capacity loss while keeping the battery operational and allowing for some self-discharge.

http://batteryuniversity.com/learn/article/how_to_store_batteries

The garage will stay still.  Charged it is. 

Thanks!
J. Ice

Maybe a silly question, but any thoughts on how to effectively drain 12v battery after a day on the water?  I'm considering this in an effort to prolong the life of said batteries.  FISH finder, trolling motor ext.  I've heard it is better to keep a dead battery for long term storage than a partially charged one.  Though best is to have a battery tender hooked up (not practical).  Maybe I'm over thinking it.
Thanks,
J. Ice

You better do some more research.  It's never a good idea to store a dead battery.  All batteries have some sort of internal resistance and will eventually drain themselves.  That's why a fully charged battery eventually goes dead in storage.  At some point, the voltage will be so low that the battery is damaged beyond recovery. 
Battery tenders are also not always the best way to go either.  Leaving a battery on a tender that has a float voltage too high for the type of battery connected will cook that battery.  The best way to store a battery is fully charged.  If that can't be done, then a partly charged battery is better than a dead battery. 

The best way to store a battery is fully charged.

Absolutely not for lithium batteries.


Sent from my iPhone using Tapatalk

The best way to store a battery is fully charged.

Absolutely not for lithium batteries.


Sent from my iPhone using Tapatalk

I've got at least 10 Li-ion batteries I use for my power tools.  They are are left fully charged when I finish a project and the newest ones are at least 5 years old.  Maybe full charge storage isn't the best, but it sure doesn't hurt them.  Not in my experience. 
I also used to maintain the handheld portable radios for SMUD.  Those have Li-ion batteries.  Manufacturer says to place the radio in the charger at the end of the shift regardless of charge.  Now, that's not long term storage, but so far I've not found a definition for long term storage regarding these types of batteries.  Days?  Weeks?  Months?  These chargers would first evaluate the battery, finish draining it down, then recharge it.  The display would state the % of capacity when finished charging so I'd know if the battery was beginning to lose it's rated capacity. 

Jerry,
Let me start by saying that I'm not trying to dispute your experience with your batteries. People can draw their own conclusions on what's best for them. If anyone is interested, there are many online sources that talks about this subject of battery storage.

When I first started my own research over 10 years ago, I wanted to learn how to care for my e-bike batteries to maintain high performance. There were many people on the internet giving advice when they shouldn't have. I didn't know who to believe. So, I did my own experiment. In the first picture, there are two arrays of Makita batteries (Lithium). One array I fully charged after every run. The other array I charged them half as long as I did the first array. For the first year or so, I noticed no difference what so ever. Both arrays charge to full (20.8v to 21v) per battery. By the second year, the array that I store at full charge would only charge up to 20.0-20.5v per pack. The one that I stored at half charged were still able to charge to 2.08-21v.

One may say what's the big deal about 0.5 to 1 volt drop. Well, That one volt difference is about 20% capacity drop. If you use a true smart charger, you will see that  the last 1 volt before full contains about 20% of the full capacity. (I'm referring to Lithium batteries here. For SLA, the last 1 volt before full contains much more juice than 20%.)

The second picture I'm trying to show the effects of keeping a Lithium Polymer batteries stored at full charge. I'm trying to show the two blue batteries had ballooned after only three months. Whereas, the green one was stored at the recommended storage charge (3.8v per cell). No ballooning whatsoever. Ballooning by itself is not a problem, but it also increased the internal resistance and decreased capacity. Btw, when an equipment tells you it is at 100%, that number is meaningless. The manufacturer can interpret the voltage-capacity ratio any way they like. An unhealthy battery can charge to full, but voltage drops quickly under load. The percentage is only an approximation. Please do not depend on that number. You need to learn the characteristics of your batteries.

You mentioned your radio manufacturer recommended to put the unit back on the charger after use. If you ask me, I think they're trying to sell you more batteries down the line. My Black and Decker lithium screw driver stated do not keep the screw driver in the charging dock. So I guess different manufactures can recommend whatever they want.

I'm saying all this is not to dispute, but people should do their own research if they want to know how to care for their equipment. Different battery chemistry require different care. A blanket statement that says all batteries should be kept at full charge is simply not true. If that is true, why do most smart lithium chargers have a Storage Charge function? Maybe it's a gimmick to trick people like me into buying things like the ISDT FD-100?

Tight lines,
ernest

The best way to store a battery is fully charged.

Absolutely not for lithium batteries.


Sent from my iPhone using Tapatalk

I've got at least 10 Li-ion batteries I use for my power tools.  They are are left fully charged when I finish a project and the newest ones are at least 5 years old.  Maybe full charge storage isn't the best, but it sure doesn't hurt them.  Not in my experience. 
I also used to maintain the handheld portable radios for SMUD.  Those have Li-ion batteries.  Manufacturer says to place the radio in the charger at the end of the shift regardless of charge.  Now, that's not long term storage, but so far I've not found a definition for long term storage regarding these types of batteries.  Days?  Weeks?  Months?  These chargers would first evaluate the battery, finish draining it down, then recharge it.  The display would state the % of capacity when finished charging so I'd know if the battery was beginning to lose it's rated capacity.

Lithium ion can be stored fully charged.  Lithium polymer need to be brought down from fully charged (4.2) volts per cell to (3.7) volts per cell for storage.

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Here is an old post:

http://www.norcalkayakanglers.com/index.php?topic=69010.0