Need some battery pack help please.

OK, so I have several Xepa Technology XP645 solar rechargeable lights that I need replacement battery packs for. They were never used and have been sitting in the box for about 2 years. The battery cells have swelled up and are no good. The manufacturer wants about $50 per pack plus shipping, so I am hoping to come up with a different solution. Here are some pictures of the pack:







First off, what's the deal with the Yellow wire? Is it a temperature probe or other feedback lead?

I am hoping to replace this OEM battery pack with something that I can find off the shelf somewhere. My first though is to use a pair of unprotected 18650 Li-ion cells tabbed together in series. Does that sound like a reasonable solution? There is plenty of room in the fixture for them. Do I need the Yellow wire connection, and if so, where does it go?

Any thoughts or suggestions are most welcome. Thanks!

Peter

It looks like the yellow wire is a balancing connection, i.e. it is connected between the two batteries.

I can give you a little help, some others will help you more...

Their are 2 serie 2 paralell pack, so I will recomend you make you own pack exactly like this with some unprotected 18650 like you say, buy a name brand like; lg, sanyo, or panasonic.

Maybe this pcb is ok, if not you can replace it too.

Checking close the pic, the yellow wire is for charge the batteries, their are connect in a way that the pcb charge in two groups the batteries.

Sorry, I am not sure about the yellow one, like I say before, I think that is for check the voltage in the two groups of batteries...

In ebay I see some sellers offering the batteries with the taps that can help and make it easy to build...

SFMI4UT

Thanks for the replies guys. I don't think 4 x 18650 cells will fit in the compartment, so the 2 series 2 parallel pack idea is out. I was hoping to just be able to use the 2 x 18650s in series. If it weren't for the yellow wire, I don't think that would be a problem, but I don't know exactly what that connection does. I wonder if the light would function if I just don't use it?

The batteries recharge from a small solar panel so I'm not really worried about the battery balancing between the two cells. Should I be?

LitFuse said:

The batteries recharge from a small solar panel so I'm not really worried about the battery balancing between the two cells. Should I be?

Click to expand...

With normal LiIon batteries, it is important to keep the cells in balance.
I do not see the problem with the yellow wire, it is just connected between the two cells in a series connection, why not do the same again?

The yellow wire might allow the PCB to read the Voltage of the first cell only so it can compare its' Voltage with the overall pack Voltage and determine the balancing required. If it knows cell #1 Voltage and the pack Voltage, then it knows cell #2's Voltage. I cannot tell but many of these PCBs perform on-board balancing when the pack has just finished charging and the charger is disconnected. Knowing both cell Voltages, it uses power from the highest Voltage cell to continue "charging" the lowest cell until they are equal Voltage.

Where does the yellow wire ultimately go? Is there something in the circuit that requires only 3.7 Volts as opposed to 7.4V?

Thank you for your replies gentlemen, but it looks like I've lucked out!

Lithium Polymer Rechargeable Battery

Peter

I have the same type of battery, blown, it does not turn the light, it has plenty of voltage on the battery and also the solar cell it putting good voltage any clues?

I have the same problem the batter blow out, it has plenty voltage but it does not turn on the light any ideas? What is the yellow wire for?

LitFuse said:

[...]

First off, what's the deal with the Yellow wire? Is it a temperature probe or other feedback lead?

Click to expand...

"BM" means Battery Middle. On a 2S pack it is connected in the middle of the two series cells so that the voltage of each cell can be measured (for balancing, per-cell under/overvoltage protection, etc).

Greetings, question how can I find a replacement battery and reconnect the third wire? most batteries are two wires, can someone give me an idea to rewire.

Greetings, well I bought two 4 battery holders and use a 18650 batteries with 3000 Mah and built my battery pack for the XP645 light and it is working fine. I adapt the batteries inside. !!!

Congratulations! If you share some photos of your solution they will probably prove helpful to others with similar needs.