[Closed] Replacing cells in a tired battery - Anyone done it ?

The tags are spot-welded onto the end of each cell - you should be able to solder to the tags, but you will need a BIG soldering iron so you can make the connections without putting heat into the cells as you solder and/or use a heat sink on the tag to protect the cell.

Would a small blowtorch be any good instead of a soldering iron?

Could a conducting adhesive be used instead of soldering to stick the tags on? (is there such a thing as a conducting adhesive?)

Would a small blowtorch be any good instead of a soldering iron?

If you're new cell does not have tags (you can usually buy them with or without), then you can solder directly to the end fo the cells, but all of the above still applies, though more so!

I thought about this last year and read some stuff about it, the tags are kind of welded on to the battery IIRC and it is best not to mess about stripping and re building the 18650 batteries which you would have to do as they have individual protection circuits that will have to be removed for the overall cicuit to work.

If your battery is not totally FUBAR then drop smudge from mtbbatteries an email and he may be able to help you by replacing the dodgy cells.

Alternativly do waht i did and just buy a battery from him. My battery was well beyond repair - cells had leaked and other horrible stuff.

If your battery is not totally FUBAR then drop smudge from mtbbatteries an email and he may be able to help you by replacing the dodgy cells.

Alternativly do waht i did and just buy a battery from him. My battery was well beyond repair - cells had leaked and other horrible stuff.

This is defo sound advice!!!

It's dated 2005 and it's had at least 3 years use for regular night riding so I guess the cells are all tired.

I didn't realise the cells had protection circuits in already, I guess I can't just wire the 8 cells up without the extra protection circuit? Or is that likely to lead to fireworks while charging?

The easy answer is to go to Smudge.

However I've just built my own 6 x 18650 battery pack using this battery holder http://www.luminousdiy.com/Light%20Kits%20and%20Parts.htm#holders

I thought about soldering connections direct to the batteries, but was concerned about heat and wires actually sticking. The main thing that put me off though is being unable to replace cells if doing a long endurance event. Using a holder I can run Trouts DIY 1800 lumen light on FULL all through the night only using 12 batteries in all.

Is it just a protection circuit or actually some driver for the LED's that you can see? Either way you could still wire it in to a new battery setup. You can now buy individually protected cells (which appears to be the norm to be honest)

The benefit of building your own pack is that its cheap, mine came in at £30 ish for batteries, charger and battery holder. You can replace cells cheaply in the future as and when needed, and you can create a spare battery pack for peanuts ie buy more cells.

The drawback is that it uses DX parts, and I have had trouble with the charger, which to be fair DX are replacing FoC so I now have 2 charges even though one is slightly knackered.

I am no expert and would strongly advide dropping smudge an email. However i think simply wiring up the batteries will cause you problems, as FunkyDunc suggests getting a battery holder will be a simple solution and avoid any fireworks. You would need to charge the batteries individually.

Building packs from NiCd or NiMH cells isn't a problem - you just need a big iron to solder to the cells without killing them, as already mentioned. I've rebuilt my old Vistalite Nightstick packs a couple of times using cheapish NiMH - double the original capacity, last time cost me around £30 I think. I've got a 50W iron I bought for soldering batteries when I was into r/c cars - that works fine. You'd struggle with a normal 25W one - if it's not powerful enough it takes too long to make the joint and the heat spreads into the cell too much.

Lithium cells are more dodgy.

Hi Andy,

You have a mixed batch of cells there by the look of it (different coloured sleeving).

All cells are best being from the same batch for a start. Basically each cell has to be off the same capacity/ voltage (charge state) before assembly, that way the 'pack' as a whole will have each cell being charged and discharged at the same rate.

If you have one cell at say 3.9V and the rest at 3.7V the protection circuit will trip when the 3.9V reaches its full charge voltage. but the rest of pack isnt fully charged, and on discharge the lower voltage cells will end of discharge voltage sooner and trip the circuit.

Plus it would be best having the cells welded rather than soldered together,

If you want to email me, please feel free to do so Andy, just fill me in on the details of your new light and battery required.
Thanks

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Thanks for all the info chaps. It's for one of Trouts Liberators so needs to be a decent size pack to get a couple of hours run time on full power.

"FunkyDunc - Member

However I've just built my own 6 x 18650 battery pack using this battery holder http://www.luminousdiy.com/Light%20Kits%20and%20Parts.htm#holder s"

Thanks for the link, I think I'll try a couple of these cell holders and bodge a pack together. I have a charger for the individual cells. If that doesn't work out well then I think a pack from Smudge is on the cards.

No reason why it shouldnt work, I had no problems soldering the contacts.

Have you sourced 18650 batteries yet? There appears to be all types of conflicting views as to which DX once or best, or whether they will last any thing like as long as non chinese made ones.

Just to note, the comms with the battery holder guy is almost none existant, and one day it just turned up on my door after about 3 weeks of ordering.

This is the only guy I could find any where in the world though who made 18650 battery holders.

There was a note on his website saying he was only taking orders up to 1st October then he would only be supplying existing trade customers. Sounds like he's not making money from it, which seems a shame. The amount of people using 18650 cells should mean there is a market for a product like that.

The cells I'm planning on using are the blue ones in the photos in the OP (Trustfire 2500mAh). The grey sheathed ones are older cells that have started leaking/rusting. I got them from ebay and they worked OK in the two DX p7 torches I was using (before they both packed up 🙁 ). They've not had much use so they hopefully should be OK in those holders.

I make my own batteries by cutting the existing soldered on tabs on laptop batteries bought on ebay and resoldering the tabs (hence no soldering directly to the cells). I'd suggest that trying to solder directly to cells is a bad idea. Taking cells from an existing laptop pack ensures good matching - I also use a balancer when charging, but reckon I'd be OK without it. If anybody else is interested in that route I've always got Dell 66Whr packs as they seem to offer the best value (if a little down on state of the art cell capacity) - when I first started doing this it was far, far cheaper that way than any way of buying individual cells.

The trouble with battery holders is that they're susceptible to vibration and tend to have extra contact resistance.