Up until about a year ago I worked at a battery store, often rebuilding drill packs and Roomba batteries and the like, so when a battery at my local hackerspace (JaxHax) went kaput I decided that I could rebuild it far cheaper than buying a new one. You can use this same basic method to rebuild all Ni-Cd and Ni-MH cordless tool batteries as well. Essentially I took a cheap no-brand battery with suitable cells and transplanted them into my other battery's shell.

The pack came from harbor freight on sale for 15 bucks, and for 15 cells  at 1500mA that's pretty good. Whether these are long lasting quality cells or whether they crap out before long we'll have to wait and see, but it's worth a shot. Stock DeWalt packs have 2000mA cells, so this is only 75% the original runtime, but for most things around a hackerspace it's suitable.

Anyway, As you can see from the photos, I opened both packs, removed their cell "cores", cut the new cells into 7 pairs with a dremel, then imitated the original cells layout, soldered desoldering wick where I needed connections, and salvaged the casing, screws, thermistor, and connector from the original pack. For the cell connection on the front end of the pack I used a peice of springy nickel coated steel from an RC car's controller switch as the negative cell's contact didn't have a tab to solder to and soldering to rechargeable batteries is not a good idea and difficult even if you try.

The sharpie marks across the tops of the cells are more just as a reminder and guide while you solder your wick tabs in place, but aren't needed. If you have any questions feel free to ask!
<p>How are the HFT cells holding up?</p>
<p>At the risk of sounding stupid, why not just transplant the cells as they are and connect the positive and negative wires? Is it because the cells do not fit in the harbor freight configuration?</p>
<p>Right, that is why. HFT packs tend to be flat, and Ryobi's oneplus packs have one cell sitting in the stem of the pack that goes up into the tool.</p>
<p>Oh damn. I am supposed to pick up a replacement ryobi from HD today. I paid $50 for it. Now I'm super tempted to just return the battery and do this.</p>
<p>If you can afford it a lipo setup its way better, lipos are cheaper to buy and half the weight of NiCDs they also run at near constant speed till they get very low on power and charge fast.</p><p>Putting in the cells is easy and after soldering a connector to the existing terminals its all plug and play, you just need to make a hole somewhere around the top(the part that is covered by the drill) so you can plug a balance cable into your charger.</p><p>You need to buy a hobby grade lipo charger like an imax b6 which puts the price up a little.</p><p>Got my 5s 18V battery from hobbyking for 1/4 of the cost of a ryobi battery.</p>
<p>Just a note to let you know I have added this to the collection: Cordless-Drill-Battery-Maintenance !</p><p>&gt;&gt; http://www.instructables.com/id/Cordless-Drill-Battery-Maintenance/ </p><p>Take a look at a bunch of different/similar approaches to this project.</p>
<p>Why didn't I think of that?? Great idea, Harbor Freight here I come. I have a Skill battery that is pure crap. A transplant is in order. </p>

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