# Using Lithium to replace 'deep cycle' LA batteries



## lowcrawler (Jun 27, 2011)

We have an application where a single, normal, deep cycle LA battery lasts about one month. Draw is zero most of the time with slight draw (like 150W or something) for about 20 minutes a day. 

We charge the battery with a small solar panel - meaning we basically only need to head to the site once every few years to replace the battery.


I was wondering if this might be a good place to use prismatic lithium batteries the likes which go in my EV. Main concens being over charging via the solar panel without some sort of 'smart charger' or something (right now it just trickles on in... given the LA does decent with over-charging)

Any recommended products or setups?


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## Ziggythewiz (May 16, 2010)

I'd stick with lead. Lead really likes slow/trickle charging and is very forgiving for slight overcharging. 

Lithium's main advantage is energy density, which doesn't matter much in a stationary applications.

Set and forget for a few years sounds pretty reliable, though you might get even better life if you check fluid levels every 3-6 months. What is driving the interest to switch?


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## lowcrawler (Jun 27, 2011)

Ziggythewiz said:


> What is driving the interest to switch?


For the solar stations where size isn't an issue -- not much. Probably just a lower overall cost (hopefully).

For the solar stations where size IS an issue (these are remote enclosures, some are pretty small) it's the size advantages. Lead has been working, but if there is a better solution... might be worth a shot.

The main drive is for installations where solar is problematic (ie: very very little sunlight, or no solar panel at all)... so the lack of self-discharge of Lithium combined with the higher energy density might help us get through, say, a 6 month winter without needing to head to the station and swap batteries...


Sounds like Lead might just be the better option all around though...


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## Ziggythewiz (May 16, 2010)

Some of it depends on your power production to capacity ratio. 

I once killed a DC battery that was on a cheapo charge controller (45w panels) because my TV viewing habits changed, so the battery got too full and gassed to death over the summer (I didn't know how to maintain it at the time).

I currently have a 5w panel on my ACC batt with no controller, but because the input to capacity ratio is so low I could leave it on there forever and it wouldn't hurt the battery.

If you are putting in enough power to need a good controller, a lithium one would likely cost the same as a lead one, but if you already have lead controllers, there's that replacement cost to consider as well.


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## icec0o1 (Sep 3, 2009)

I disagree with Ziggy and would say Lithium is definately the way to go. More expensive up front but definitely less long term. Lithium is the chemistry which likes slow trickle charging, lead does not and it actually causes sulphation. 

There are plenty of cheap 12V and 24V lithium chargers, especially low amp ones so you have nothing to worry there. All you have to do is calculate what AH of batteries you need which can provide the maximum draw you require. The math is fairly simple: 3.2*4 = 12.8V 150W / 12.8V = 11.7 amps. So if you had a 2C battery, you'd need it to be at least 6 or 7 amp-hours and it should provide the power for about 25 minutes for 83% depth of discharge.


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## EVfun (Mar 14, 2010)

LiFePO4 does NOT like trickle charging, full is full and any additional charge is damage. 

Lead acid batteries are not sulfated by trickle charging. Lead sulfate is what the surface of the plates are converted to upon discharge, which is why they can freeze more easily in a discharged. Sulfation, when referring to a Lead acid battery, is the process of the amorphous PbSO4 turning into the crystalline form. This causes in a permanent loss of capacity. 

Lead acid batteries have been used in trickle charge applications for years in the telecom industry. They last about 10 years if the charge voltage is limited to about 2.25 volts per cell (temperature compensated.) Flooded lead acid batteries can manage nearly the same life with less regulated voltage if the current is limited to a low level.


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## icec0o1 (Sep 3, 2009)

EVfun said:


> LiFePO4 does NOT like trickle charging, full is full and any additional charge is damage.


Okay, I used the wrong term. I meant very slow rate of charging from a solar panel.



> Lead acid batteries are not sulfated by trickle charging. Lead sulfate is what the surface of the plates are converted to upon discharge, which is why they can freeze more easily in a discharged. Sulfation, when referring to a Lead acid battery, is the process of the amorphous PbSO4 turning into the crystalline form. This causes in a permanent loss of capacity.
> 
> Lead acid batteries have been used in trickle charge applications for years in the telecom industry. They last about 10 years if the charge voltage is limited to about 2.25 volts per cell (temperature compensated.) Flooded lead acid batteries can manage nearly the same life with less regulated voltage if the current is limited to a low level.


From my experience, if you have a deeply discharged lead acid battery, it's not a good idea to charge it up slowly. Yes, if you have a Lead Acid battery which is always at 100% and drops to 95% for a few seconds 5 times a year, it'll last 10 years with a trickle charging. But that's not lowcrawler's situation.


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## Ziggythewiz (May 16, 2010)

icec0o1 said:


> Yes, if you have a Lead Acid battery which is always at 100% and drops to 95% for a few seconds 5 times a year, it'll last 10 years with a trickle charging. But that's not lowcrawler's situation.


Are we reading the same thread? 'Cause that's about what he said.



lowcrawler said:


> Draw is zero most of the time with slight draw (like 150W or something) for about 20 minutes a day.


He needs about 45 watt hours a day...that'll leave almost any DC battery at 95% or more.


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