Replace Li-Ion cells in battery pack?

have an 18V 2.4AH battery pack for Ryobi power tools that will no longer take a charge and that the charger indicates is defective.

I've taken it apart and found that it has five pairs of cells that are labeled:

"LS IMR-18650BB YT0288. Made in China"

I see on line numerous variants of the 18650 cells with various mAH ratings but nothing with the "BB" suffix.

Four of the pairs of paralleled cells show a voltage of 4.1x; the other pair shows 2.1mV.

Is it worth the effort of trying to replace the defective pair, or is there a way that I could try to restore them to life?

If I want to replace the defective pair, I assume that any 18650 cells with at least 1200mAH capacity will work -- but in fact I don't see any that low.

I don't have a spot-welder. If I use a Dremel cutting wheel to cut the tabs on the defective pair, would it be OK to solder new ones in place using copper flashing?

Perce

I totally agree with Clifford Heath. However, let me add a few additional comments.

The cases on most 18650 cells are stainless steel. You won't be able to solder to those. Copper flashing might make a connection, but at the high currents involved, will probably give you intermittent connections, corrosion, or heating problems. Spot weld or forget it.

You can buy 18650 cells with tabs that can be soldered:

I do something different, which might be of interest. Instead of using 18650 cells, I use flat cells usually used in model airplanes, cars, quadcopters, etc. Something like this: The listing are for 5 cell batteries (5S), west coast warehouse, and sorted by ascending prices. If you're lucky, you can find a 5S battery pile that will fit in your Ryobi battery box. If not, you can bash a big hole in the battery pack and improvise.

Note that all the batteries have a "balance charger" connector. I won't go into detail now, but basically this is the way you avoid killing a battery pack. Each cell is monitored individually with no risk of overcharging any of them if another cell is low voltage. The technique is SLOOOOOWLY creeping into the power tool biz.

If you decide to go this route, bug me as there are a few other things that you'll need (power connector/adapter, balance charger, etc).

There are many variants of cells. The ones designed for high current have lower capacity. If you try to use laptop high capacity cells in a drill, you'll have low performance and short service life. You're likely to find that the correct cells you need cost about the same as a new pack.

You can try to charge the dead pair with a 4V power supply current limited to 100 ma or so. Always wear eye protection! Don't get in a hurry, or you may set the thing afire. Do it in the garage in a bucket that can't burn if the cells catch fire or explode. I've had limited success with that in laptop packs. But don't get your hopes up. If it works, charge each pair individually to the same voltage. Don't get in a hurry, it may take a long time for the current to drop.

NO, get the right type of HIGH current cells and replace them all.

DO NOT SOLDER DIRECTLY TO ANY CELL OF ANY KIND. You can solder tabs together, if you're quick about it.

What's your objective? If you want to play with battery packs, you're on the right path. If you want to drill holes reliably, call up Ryobi and buy a new pack. Last year at this time they all seemed to have lifetime battery guarantee.

If you're in the US, you might check with your local Batteries Plus store. I had some DeWalt 12 V NiCd packs rebuilt by them for pretty reasonable money, a couple of years ago. They have cells with tabs, and the spot-welder to correctly join the tabs together.

Home Depot sells a brand new Ryobi P105 battery - probably the same one you have - for $59+tax. That listing also claims that the battery has a 3-year warranty; is it possible that your battery is younger than that?

Standard disclaimers apply: I don't get money or other consideration from any companies mentioned.

Matt Roberds

When did your need for five cells become ten?

To my knowledge, no-one has worked out how to make a 4AH 18650 cell yet.

The best cells are below 3.5AH, and five of those are already more than $49 without building a case. Ryobi is Chinese now, so they're almost certainly lying.

If you value high capacity, buy your own branded cells.

If I have to get a matched set -- of ten (five *pairs*) -- rather than of two, I might as well get two 4AH ones for $99.

See above.

This battery pack does have connections from every between-cells connection to the PC board, so I am assuming that this was supposed to be part of the balancing circuitry.

I can buy two of the 4AH packs for $99, so replacing all ten cells (five

Perce

I did ask at my local Batteries Plus, who told me that they don't rebuild Li-Ion battery packs. Their after-market battery packs are outrageously expensive.

The defective one is a P104, and I have no idea when I bought it. Even if it were, theoretically, in warranty, I've voided the warranty by taking it apart and peeling off the adhesive foam covering the ends of the cells; it never occurred to me that it *might* still be in warranty. It appears that Ryobi warranty service is obtained by returning items to a service center -- no indication that one can simply exchange a defective item at Home Depot.

A two-pack of the 4AH P108 packs is only $99. I don't know whether that's a year-round deal, but I did take advantage of the same deal around this time last year. I suspect that's a year-end deal, as a single P108 is the same price.

Perce

I wasn't aware of that. Progress lurches forward, usually when I'm not looking.

This might be of interest if you want to repair your battery pack: "Cell Re-balance of Ryobi One+ 18V Li-ion Battery (130501002)" "Rebuilding Ryobi 18v Batteries" Looks like the balancing circuitry is in the battery pack, not the charger.

I would not trust the battery capacity (ma-hrs) as stated on the label. However the goood price and less risk of buying these is probably better than trying to rebuild a pack.

I might try that.

He deals with minor voltage differences between cells, not the huge differences I have (mV only, from the one paralleled pair).

Any less trustworthy than the alleged 2.4Ah capacity of the present one?

Perce

Well, I don't know if Ryobi tests their cells, where they get them, or what they're charger is doing to them. If they're like most laptop and UPS computah battery manufacturers, the prime directive is to quickly kill the batteries in order to sell the customer a replacement battery or UPS. I suppose cordless tools are much the same.

If you want the best cells, various individuals have already done the work: Also, search on candlepowerforums.com for battery tests:

I do my own using a West Mountain Radio CBA-II. For example, here's an Ultrafire 3000 that manages to barely squeeze out 850 ma-hrs at 1C: I know garbage when I buy it.

Note that your 2400 ma-hr battery is usually rated at 0.2C or 480 ma discharge current. The test is also at room temperature. Vendors sometimes cheat and test the batteries in a water bath. The problem is that your drill probably draws about 30A, split between two strings of cells or 15A per cell, or about 6C. If you look at the typical LiIon 18650 family of curves, 6C isn't even on the graph. Much depends on at what voltage you want to declare the battery to be discharged. Panasonic uses 2.5v. Good quality LiIon batteries do not loose much capacity at these discharge rates. Junk drops drastically in capacity. Without knowing more about what you have, and testing the cells, I can't guess(tm) the capacity at 15A discharge.

Incidentally, if you're considering buying or building a battery spot welder (I am), this might be interesting: I made my own CD (capacitor discharge) system, but it sucks and is in need of replacement.

Good luck.

The flux I bought in a plumbers supply yard works perfectly OK on stainless, but sometimes needs the stainless to be lightly abraded.

Often I see a warning on lithium cells not to expose to more than 212F - or boiling water in other words.

Whenever I need to solder lithium cells; I just trim back the stainless strip so it still has a bit spot welded to the cell - its just that little bit more thermal resistance between the iron and the cell.

A fully charged cell can provide a fair bit of entertainment if the heat of soldering melts the seal and causes a short - solder first, charge later.

Paste or liquid flux? I've had no luck soldering stainless with either. Mostly, I try to solder to button cells, not 18650, which might be different. The paste flux made for copper pipe doesn't seem to work for stainless. For example; Can be used on all materials except aluminum and stainless steel.

I tried boosting the voltage of the low-voltage pair but without much success so far. I don't really have a suitable power source.

When I plug that pack into a P117 charger, the red light flashes "for ever" ("Testing"), but after a looong time changes to the slow flash indicating "Defective." When I plug it into a P125 charger, I get the "Charging" indication for just a minute or two, then it switches to "Charged," but of course it isn't: that one pair of cells still shows only in the mV range.

Perce

It's not clear how those welders work. Looks like timed pulse??

I spent a LOT of time messing with battery tab welding. You need a LOT of heat QUICKLY. I put a SSR on the primary of a modified microwave oven transformer and counted the number of cycles of 60 Hz. to set the power delivered. Problem with low voltage is that it is extremely sensitive to resistance in the path. I could get very good welds about 80% of the time. On average, I got all good welds on about 0% of the packs.

You really want a fixed amount of energy delivered independently of contact resistance.

Capacitive discharge is the way to go. But, to get repeatability, you need to be switching the energy at high voltage. It's not easy to switch 1000 amps or more.

I gave up on DIY when I found a 125 Watt-Second CD system on ebay for cheap. That puppy can put 7000A single pulse into .001 ohms. Repeatability improved dramatically. Battery doesn't even get warm.

Reread my original message in which I referred to four *pairs of paralleled cells* showing 4.1x Volts and the other *pair* showing only

That's why they use *paralleled pairs* of 18650 cells.

BTW, a few years ago I found a Web site dealing with battery packs for power tools that reported that all the packs they had disassembled used the same Sanyo 18650 cells -- including the RIDGID packs with the lifetime warranty and the Craftsman "19.2-volt" (for how many seconds after they come off the charger?) ones.

Perce

Some plumbing is stainless and any good plumber's yard will stock flux for it.

The one I bought from had regular and active flux - I bought the latter and it works just fine on stainless.