Rebuilding a Frog style Battery

[jimmyN]

My battery (48V 9AH) started to fail a few months ago it runs for twenty minutes or so and stops, no lights on the indicator. After charging just a few minutes it showed a full charge. I posted a message and the general consensus is the battery most likely has a bad cell or two and is telling the BMS to shut down.
I dissected it and it looks like it has the flat silver foil encased type of cells. what type of cells are they? is it worth rebuilding? I love the style of this battery it fits perfect under my seat and super easy to remove. These battery's are not expensive to buy but if there are better cells available that will fit in the case maybe rebuilding is a good option? does anyone rebuild these?
I live in central california

 

[tomjasz]

Pictures tell a better story, but you probably have LiFePo4 cells. If you can't find the same cells you'll likely need a new BMS to change to 18650 cells.

How old is the battery?

 

[jimmyN]

two- three years, I bought it used

 

[jimmyN]

Pictures tell a better story, but you probably have LiFePo4 cells. If you can't find the same cells you'll likely need a new BMS to change to 18650 cells.

How old is the battery?

 

[Jimboyr6]

Unless you want to find the low cells possibly 1or2 u be better off getting a new 18650 pack,once lifePo4 gets old its a pain to keep in line.

 

[motomech]

I could fit quite a bit of Multistar LiPoly in that case.

 

[jimmyN]

I ran the battery down until it quit (about 5 minutes of moderate load) i disassembled it and metered between the groups of cells and all were within a few volts totaling 53 volts going into the BMS what other tests should I do to trouble shoot?

 

[jimmyN]

I could fit quite a bit of Multistar LiPoly in that case.

Is this a better cell than LiFe?

 

[Hillhater]

I ran the battery down until it quit (about 5 minutes of moderate load) i disassembled it and metered between the groups of cells and all were within a few volts totaling 53 volts going into the BMS what other tests should I do to trouble shoot?

Is that 53v a typo ?.....i thought this was a 48v pack ?
How many "groups" of cells are there...and how many cells in each group ?

 

[jimmyN]

I ran the battery down until it quit (about 5 minutes of moderate load) i disassembled it and metered between the groups of cells and all were within a few volts totaling 53 volts going into the BMS what other tests should I do to trouble shoot?

Is that 53v a typo ?.....i thought this was a 48v pack ?
How many "groups" of cells are there...and how many cells in each group ?

No typo 53 volts fully charged. I believe that's normal. Just like a fully charged car battery is 13.2 ish

 

[jimmyN]

It looks like 39 cells in groups of three

 

[Hillhater]

So the pack is still at 53 volts after you have run it until it quits ????
What was it before you started ?
..and it is a 13s pack ? ..with each cell group at a similar equal voltage ...But " all within a few volts" is not good. You must measure to 0.01volt units
So it must be LiPo cells
But Not like any 48v pack i know !

 

[jimmyN]

So the pack is still at 53 volts after you have run it until it quits ????
What was it before you started ?
..and it is a 13s pack ? ..with each cell group at a similar equal voltage ...But " all within a few volts" is not good. You must measure to 0.01volt units
So it must be LiPo cells
But Not like any 48v pack i know !

It it starts at 54 right off the charger I'm not sure of the cell type there are no markings, the voltage of the groups are 4.14, 4.12, 4.14, 4.14, 4.14, 4.14, 4.14. the way I measured the groups is by metering between the small colored leads going into the BMS the charger puts out 54.7 (with no load) would the one group with .02V be enough to prevent the BMS from passing current?
Thank you for helping by the way.

 

[Hillhater]

Thats only 7 groups ?..are the others all identical ?
Can you remeasure those voltages with a load on the pack ?..to see if any of them drop significantly.

 

[Jimboyr6]

Im sure 4.15v fully charged lifepo4,is to high, iv an old stealth bomber battery 72v lifepo4 battery that would charge to 87.6v, which is 3.65v per cell,24 cell groups

 

[Hillhater]

Why do you assume they are LifePo4 ?
I cannot imagine any Lifepo4 cells holding 4.17 volts so consistently without overheating , bloating, etc.
..and the BMS should prevent overcharging anyway.
So, im guessing they are lipo.
But you need to do those load tests to see what is going on

 

[jimmyN]

Why do you assume they are LifePo4 ?
I cannot imagine any Lifepo4 cells holding 4.17 volts so consistently without overheating , bloating, etc.
..and the BMS should prevent overcharging anyway.
So, im guessing they are lipo.
But you need to do those load tests to see what is going on

Here is a better pic of the arraignment
Ill try to load test but I have noticed a significant drop in output voltage (according to my led graph display) when under heavy load as of the last few months.

 

[LewTwo]

Why do you assume they are LifePo4 ?
I cannot imagine any Lifepo4 cells holding 4.17 volts so consistently without overheating , bloating, etc.
..and the BMS should prevent overcharging anyway.
So, im guessing they are lipo.
But you need to do those load tests to see what is going on

LiPo is NOT battery chemistry.

A lithium polymer battery, or more correctly lithium-ion polymer battery (abbreviated variously as LiPo, LIP, Li-poly and others), is a rechargeable battery of lithium-ion technology in a pouch format. Unlike cylindrical and prismatic cells, LiPos come in a soft package or pouch, which makes them lighter but also less rigid.

https://en.wikipedia.org/wiki/Lithium_polymer_battery

 

[Hillhater]

Yep, its a fair cop guv ! :lol:
So, i will just stick to saying that its very unlikely they are LiFePo4 ! :wink:

 

[jimmyN]

I put it back on the charger and after just a few minutes it is showing full charge on the indicator lights mounted on the battery pack. I will try to load test tomorrow.
so if it shows one group is failing does it make sense to try to resurrect this pack or is it likely I'll just see another failure in a short period of time given all the cells are the same age.
what is the most economical way to build a battery nowadays?

 

[LewTwo]

I think that your first step is going to be diagram exactly what it is that you have.: how they are grouped, inter connections, connections to the BMS, etc. I am not a LiPo proponent but my guess is that if you are looking rebuilding that pack then replacing all the cells with new LiPo cells is likely to be the most practical alternative.

 

[jimmyN]

I think that your first step is going to be diagram exactly what it is that you have.: how they are grouped, inter connections, connections to the BMS, etc. I am not a LiPo proponent but my guess is that if you are looking rebuilding that pack then replacing all the cells with new LiPo cells is likely to be the most practical alternative.

What type of LiPo cells would you sugest and where would I buy them. I live in California. I don't have access to a spot welder but I can do a decent job soldering. one thought is to buy a pack already assembled tike this
http://www.ebay.com/itm/48V15Ah-LiFePO4-Battery-Lithium-Battery-Packs-E-bike-Batteries-Electric-Bicycle-/192028286026?
Any other suppliers??

 

[jimmyN]

Or maybe this? seems like trying to rebuild mine with better cells might not save me any money?
https://www.aliexpress.com/item/Electric-Bike-48V-12Ah-Lithium-ion-Frog-Battery-by-samsung-cells-with-charger-for-48V/32460545716.html?spm=2114.40010508.4.19.e34Dr1
Are these good cells?

 

[LewTwo]

What type of LiPo cells would you sugest ...

I wouldn't as I have no experience with LiPo. One of the reasons I have avoided them is that I could never determine what battery chemistry a particular LiPo brand/cell/pack used. There are several ES members that favor LiPo. Hopefully one of them will respond.

 

[motomech]

https://endless-sphere.com/forums/viewtopic.php?f=2&t=53796&p=800677&hilit=frog+case+lipo#p800677