BU-810: How to Repair a Battery Pack

Batteries for power tools and other industrial devices can often be repaired by replacing one or all cells. Finding a NiCd and NiMH cell is relatively easy; locating the correct Li-ion cell can be more difficult. Naked Li-ion cells are not readily available off the shelf and a reputable battery manufacturer may only sell to certified pack assemblers. Incorrect use or lack of an protection circuit could cause stress and disintegration of the replaced cell. When repairing a Li-ion pack make certain that each cell is properly connected to a protection circuit. Read about Safety Concerns and Protection Circuits.

If a relatively new pack has only one defective cell, you may replace only the affected cell. On an aged battery, it’s best to replace all cells. Adding a new cell with full capacity in between neighboring cells that have faded would cause a cell mismatch. Matching the replacement cell with one of a lower rating may work but this fix is often of short duration. Always replace with the same chemistry cell.

A well-matched battery pack means that all cells have similar capacities. An anomaly can be drawn with a chain in which the weakest link determines the performance of the battery. Read more about Can Batteries Be Restored?.

When replacing all cells, the rating is less important as long as the differences are not too large for the charger to handle. Cells with higher Ah will simply take a bit longer to charge.  The state-of-charge of all cells being charged for the first time should have a similar charge level, and the open-circuit voltages should be within 10 percent of each other

Many visitors of BatteryUniversity.com ask if NiCd can be replaced with NiMH? Theoretically, this should be possible but charging may be an issue. NiMH uses a more defined charge algorithm than NiCd. A modern NiMH charger can charge both NiMH and NiCd; the old NiCd charger could overcharge NiMH by not properly detecting full charge state and applying a trickle charge that is too high.

Welding the cells is the only reliable way to get dependable connection. Limit the heat transfer to the cells during welding to prevent excess heat buildup.

Simple Guidelines when Repairing Battery Packs

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On April 17, 2013 at 7:21pm
vikash wrote:

i have dell inspiron n5010 laptop battery and it is dead. i want to re-built it,but i confuse with volt it’s volt is 11.1v but i do not not the single cell voltage. how i found that the voltage of a single cell of my laptop battery.it has 6-cell battery,4080 mAh,capacity 48Wh, rechargeable li-ion Battery,type J1KND,

On November 27, 2013 at 12:45am
jørgen eriksen wrote:

kan ikke lsde mit nyeop det siger st lav Batterithilsen jørgen eriksen.emp.

On February 4, 2014 at 12:47pm
s cohen wrote:

can batteries exploded at certain temperatures

On March 5, 2014 at 3:30pm
bryan wrote:

I bought a new charger for my my phone the exactly like the last one but it said that the battery is not supported with the phone what can i do.

On March 13, 2014 at 12:07am
Ed wrote:

Is it the same identical battery (including model number as the old one?
Is it the same identical charger as the old one—including model number?

If THAT, my guess is that they just de-listed the old battery or old phone.  IF it is the same battery and same charger, it still is supported but they don’t list it as that anymore.  Assuming, of course, it is EXACTLY LIKE—including same model number of same manufacturer.

On March 13, 2014 at 12:10am
Ed wrote:

Batteries not only can but DO explode—about 20 years ago now, there was a rash of Ericsson Cell Phones exploding.  Also about a decade ago, Toshiba laptop batteries catching fire, which they “fixed” by reducing the capacity of the battery by half.

On April 2, 2014 at 3:59am
Chipo wrote:

how can i repair my li-ion battery for my laptop without replacing it? the battery nolonger store power

On July 1, 2014 at 5:18am
Chris wrote:

I ordered a new battery for my mid 2010 13” macbook pro from China.  It arrived DOA.  I know it isn’t the computer as it was charging the old battery before the replacement. Do you have any pointers to make a fix to this battery or test it?