18v battery repair

[Sharonjh]

Unless I can use this **broken link removed**

 

[jpanhalt]

Oh, wow. I didn't pay anywhere near that for not name brand 18650's. But then, of the options, those are the cells I had the worst luck with. Maybe cheap = crummy.

After looking at your next post, those Ultralites are what I have/had. Since you are going to solder, you might be better off with cells that already have the tabs welded. Then it is just tab to tab soldering , which has to be much safer.

 

[Sharonjh]

So it doesn't matter if the voltage on the new one is 3.7v and the other 4 are 3.6v?

 

[jpanhalt]

From what I could see of your circuit (i.e., all of the intermediate tabs to the PCB) the cells will be balanced during charging. I really wouldn't worry about that difference, since you do not know the state of charge for each cell.

Cells can come with a built in protective circuit and without. I suspect the battery pack cells don't have a built in protective circuit. I am not sure of the cells you you suggest. Probably without too. Ultrafire probably buys in bulk from any number of manufacturers, so your experience may vary. If you can find the same size cells with tabs, it will reduce your worries about soldering, as the tabs won't conduct much heat to the cells per se.

It has been awhile since I dealt with that specific size cell. I have generally used smaller capacity cells in the past couple of years, except for LiPo's for power.

John

 

[Pommie]

I would be very skeptical of the ebay 18650 batteries. See Here.

I got two 18650 batteries from Jaycar and they are fantastic. I got given some "9000 mAh" batteries from ebay and there capacity was less than 1Ah.

Mike.
Edit, the one you linked to is featured here.

 

[jpanhalt]

Mike, I share your concerns about "fake" or simply crummy 18650's from eBay.

Also, 18650's are relatively long and skinny. Mine measure about 18 mm dia. x 65 mm long (excluding the + cap). That is a ratio of 3.6 L to diameter. The batteries in post #1 appear more chubby. I visually guesstimate them to be about 2.2 to 2.6 L to diameter.

In a pack like that, it is important to use the same battery sizes. I should have been more explicit. The OP needs to measure the existing batteries, go to tables of Li-ion battery sizes, and find the correct size.

 

[Sharonjh]

Thanks for the info. I measured my batteries and the are indeed 65 by 18.

 

[jpanhalt]

Sorry,the perspective in the picture deceived me. Get a recognized brand, good quality 18650 with tabs, if possible. I personally have had bad luck with UltraFire. If you are in the US, I would gladly send you 2 that are still in their wrappers. They do not have tabs.

John

 

[Pommie]

The link I posted above shows a Ultrafire being dissasembled. They are very useless batteries.

Mike.

 

[Sharonjh]

Thanks for the offer John. I just purchased a 18650 with tabs at a cost of $15 Au. Not too fussed about the price, it's all a learning experience for me. I like to save things ending up of the scrap heap if possible.

 

[Sharonjh]

Put the new battery in and still has same problem. Runs for 20 seconds and then cuts out.