Help me understand a lithium battery


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Old 06-14-24, 06:27 PM
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Help me understand a lithium battery

To be more specific, a LiFeP04 battery. 100AH deep cycle for rv. It's nominal output voltage is 12.8. it's recommended float charge voltage is 13.5. it's recommended full charge voltage is 14.6. why? If 13.5 is above it's normal operating output voltage then why isn't that voltage high enough for a full charge? According to the spec sheet it will only reach 80% SOC with a 13.5 volt charge. I'm not saying it's wrong, I just want a little insight.
 
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Old 06-15-24, 03:42 AM
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not sure it really matters as most lifepo4 chargers should be capable of charging at the correct voltage of 3.65 volts per cell which adds up to x4 14.6 volts and the nominal voltage of 3.2 volts per cell is around a 20 percent state of charge x4 is 12.8 around the time you should recharge it.

 
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Old 06-15-24, 05:40 AM
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I was trying to get away with not having to replace the power center in my RV thats rated for lithium. My current one only charges at 13.6 volts. I read a little more after starting this thread that the higher voltage is needed to balance the cells. I should have stuck with wet cell batteries.
 
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Old 06-15-24, 08:29 AM
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You need the correct charger for the chemistry of your batteries. There are different types of lithium so make certain that you have the correct charger for your battery.
 
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Old 06-15-24, 09:31 AM
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I do not think you will regret going to lifepo4 once you get your charging issues solved would just read up on your current power center see if it has any adjustability, but lighter weight and more capacity and longer lifespan really just not really worth sticking with lead batteries.
 
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Old 06-15-24, 12:27 PM
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You'll love how the battery doesn't self discharge. You can put the camper away for months and it will still have a full charge for a trip, or whatever charge level you left the battery at. No trickle charger or battery maintainer needed so you don't need shore power when the camper is in storage.

And don't forget the weight reduction and space saved. You either will have a physically smaller battery with similar capacity to your old lead batteries. Or, you go for one about the same physical size as your old batteries and enjoy much greater storage capacity.
 
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Old 06-17-24, 07:17 AM
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"" According to the spec sheet it will only reach 80% SOC with a 13.5 volt charge. I'm not saying it's wrong ... ""

The theory behind all this, simplified:

All battery charging requires that the charger apply a voltage backwards that exceeds the present output voltage of the battery.

Typically the battery output voltage rises as the charging progresses.

In this case, when the charge level is about 80% the battery without the charger attached and with nothing else (load) connected delivers 13.5 volts. So the charger providing at most 13.5 volts will reach equilibrium with the battery and no more charging current will flow.

The significance of the charger being correct for the battery is that the charger needs to
keep the "charging speed" within certain limits. This is accomplished by monitoring the charging current (amps) and adjusting the charging voltage.

(The no-load, or open circuit, voltage of a battery may be greater than the voltage under typical loads including not so heavy loads.)
 

Last edited by AllanJ; 06-17-24 at 07:37 AM.
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Old 06-21-24, 07:25 PM
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I bought a special lifep04 charger and after my stock RV charger was "done". I put the special charger on it and it only took 5 minutes to say done as well. The battery has a bms and reads 100% soc after the special charger and 90% before it. But I find it hard to believe it received that final 10% in just 5 min.
 
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Old 06-22-24, 07:19 AM
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Lithium batteries can accept a very fast charge rate. Longer/slower charging is easier on the battery but they can be kicked hard for a quick charge.

Lithium's also charge differently. When discharged they can accept a heavy charging current. Then as they approach full the rate slows so you may see your charge state rise quickly but then notice that the last few percent can take longer. The good thing is the battery has no memory so you don't have to charge to 100%.
 
 

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