Why my new 12AH LiFePO4 battery is only charged to 5.5AH initially? Anything wrong?

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Joined: 05/27/2009
Points: 6

I've got the brand new 12AH rated LiFePO4 battery.

The smart charger I use is 2A. I used this charger before
with another 9AH LiFePO4 battery without any problem.
So I assume the charger is good.

Here is what I noticed from "WATTS UP" battery meter after charging /discharging it three times

The charging current was between 1.67A - 1.60A. became 0A toward end.
charging voltage was 53V - 55V and jumped to 60V toward the end.
charging time was about 3 hours.
The total charges went into the battery was between 5.5AH - 6AH.

the charger light turned green from red at the end and stopped charging.

If I left the battery on the charger with green light longer the charger
will turn red and charged the battery for about half minute and turned green again.

Is this normal with a new LiFePO4 battery?

Does it have anything to do with "balancing cells" with initial charge for a new battery?

Will the battery eventually be able to charge to the full 12AH after using it for a while?

I may have to return it if this is not normal.

thanks for you help.

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Joined: 05/27/2009
Points: 23
Re: Why my new 12AH LiFePO4 battery is only charged to 5.5AH ...

What is the voltage of your pack? How bout the old pack(9ah)? Do you know how many cells in series? What type of LiFePO4's are they?


-Joseph Kennedy

Kennedy Alternative Energy

Joined: 05/27/2009
Points: 6
Re: Why my new 12AH LiFePO4 battery is only charged to 5.5AH ...

it's 48v, 16 cell pack. I got it from Cammy on ebay.

something like with 12AH instead of 20AH.

I ordered 12 AH battery but they shipped wrong 9AH one. I returned the 9AH and they shipped me a new 12AH battery.
After the battery is drained. I can charge it all the way to 5.3AH and then the charger turns green, red, green red a couple of times
and stay at green even if i leave it over night. The BMS become pretty hot if I leave the charger on for a long time.

I leanred from this forum that even one of the 16 cells reach cut-off voltage such as 3.7v the BMS will shut off the charger and shold do the balancing. The BMS balancing is very slow. It usually turns red from green and start charging for 1 or 2 minutes and turns green again.

It usually stay at green for few 2 or 3 hours before it turn red again.
right after charning the pack voltage is about 60v, then gradually change to 55.6v if you take it off charger for over 4 hours.
it seems the BMS doesn't switch between green and red frequently enough.

I did manage to increase the capacy by doing following manually.
I unpluged the charger after it turned green first time. Let BMS cool down for about 3 - 4 hours.
The pack voltage came down to 55.5 -55.8v. and I plug the charger back on.

The charging process will restart and charge for only about 10 - 15 minutes and turned green.
I just unpluged it again and waited for 3 -4 hours and replugg the charger on.

By doing so I could still put more charges into the battery.
But there is long waiting before the pack voltage come down from 60V to 55.5 -55.8v to allow charging again.

I did it for about a week. Now the max 1st time charge can go all the way up to 7.1AH instead of 5.3AH now.

I still keep doing it hope the accumulated charging can go higer and higher, and eventually reach 12AH.
Now even I wait for 4 hours i can only have 5 minutes insead of 10 minutes red light time before it change to green and stay at green for a long time.

The is manully balancing charging. The BMS should do better.

Is this battery going through the pre-conditioning or initiall balancing stage?

Should I ask for a new BMS?

thank you for help


Joined: 11/22/2006
Points: 1411
Re: Why my new 12AH LiFePO4 battery is only charged to 5.5AH ...

LiFePO4 cells normally come from the factory at a partial state of charge. So, your first charging being about 6 AH is probably normal. Don't discharge the pack below 2.5 volts per cell. You will probably put a full 12AH of charge in them unless you discharged the pack to a harmfully low level.

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