Bosch Cordless Drill: New Batteries or New Drill?

[Jack Pinkham]

My Bosch 3960 24 volt cordless drill is working fine, but one of the batteries is only at 7 volts after charging, and the other is around 22. New batteries go for $65- $100 each, depending on amp-hours and whether they are ni-mh or ni-cad. This drill model was rated at 500 in-pounds torque.

So the choice is between buying new batteries for my old 3960 or springing for a new impact driver drill set which comes with two lithium ion batteries and a charger.

I took the worst battery pack apart to measure cell voltages. A majority of the cells are bad. Rebuilding the battery pack seems like a hassle, and the cost of having them rebuilt is about on par with a new battery.

New 3 amp ni-mh batteries for the 3960 would be a big improvement.
Not positive that the Bosch charger would be good for ni-mh, though.Seems wasteful to toss a good drill, but that might be the best decision from a cost standpoint.

Any suggestions?

[Dave Houseal]

I had the same dilemma. I had a dewalt 14.4v that I loved. But the price of batteries is so high it is almost not worth it. Ultimately I ended up replacing it with a new 18v kit when HD had one of their big sales.

For me adding the impact driver, recip and trim saw tipped the balance even though it was a lot of extra money. If you don't have the impact driver I HIGHLY recommend it.

[Bruce King]

I have the same drill. Its 10 years old. I dropped it 6 feet on concrete while wiring my house and it did not seem to hurt it but it must have cracked the main transmission housing because it developed looseness over the next 8 years to the point where I quit using it. The part is $85 and not worth it since my last battery could die at any moment. I have one good and one bad battery. The battery also works in a circular saw. This is a very powerful drill but too heavy for general woodworking so I bought two of the Porter Cable 18V drills so I would have 4 batteries, two chargers and would not have to worry about having less than two good batteries for a long time.

[Jamie Buxton]

Look into getting the battery pack rebuilt. The rebuilder puts new cells in the pack, generally for lots less than the OEM sells new packs. OEMs seem to think they have captive customers.

[Greg R Bradley]

I have one that lives at work and has been adopted by an employee. It has been in regular use for 8 years and still works perfectly. If it fits your need, put new cells in the battery case or pay someone to "rebuild" it.

I bought an 18v Li-Ion and prefer it for general use as it is lighter. I bought the 36v Bosch drill at a Bosch event and it is about the same weight as the 24v Ni-Cad and much more powerful. I bought it for the same price as the batteries, which I needed for my Bosch 36v Rotary Hammer. That thing is incredible.

[Ted Wong]

On the positive side I got a promo from Rockler the other day. Looks like Dewalt is clearing out old inventory and need to get rid of all their Nicad and Ni-mh to make room for the next generation of lith-ion tools. The promo offer, bring in any old cordless tool for a $100.000 off coupon on select Dewalt xrp cordless.

[Will Overton]

If it's the only tool you own using that battery it's time for a new drill.
If you have other tools that use that battery, rebuild the batteries.

[Jack Pinkham]

Thanks for the suggestions! I definitely want to get one of the new generation of impact drivers or driver/drills . However, I just remembered reading a suggestion about scavenging the battery cells from a new Harbor Freight 18 volt battery pack. They are on sale for less than $10, and they have 15 cells for transplant. It seems worth a try. If I botch the job, it's not a big deal.

[Andrew Joiner]

Thanks for the suggestions! I definitely want to get one of the new generation of impact drivers or driver/drills . However, I just remembered reading a suggestion about scavenging the battery cells from a new Harbor Freight 18 volt battery pack. They are on sale for less than $10, and they have 15 cells for transplant. It seems worth a try. If I botch the job, it's not a big deal.

Great idea Jack,
Let us know how that works out.

Wouldn't it be great if the battery packs were universal and one size fit all tools?

[Jack Pinkham]

The transplant of Harbor Freight ni-cad batteries to my Bosch 24 volt drill seems to have been successful. I still need to see how they hold up in use, though. I bought two HF 18 volt batteries for about $20 total. Even though the Bosch battery had 7 or 8 good cells, I decided not to reuse them, except for the one connected right at the terminals, which would have been a little harder to replace. Keeping the original pack together provides a template for assembling the new pack.

There are lots of websites, primarily RC hobbyist sites, describing how to solder battery packs. I found that a utility knife and hammer were effective at separating the spot-welded battery clip connectors. The cell connection points and the clips were tinned before trying to solder them together. The solder points on the cells should be abraded. I used a Dremel sanding wheel. Flux is required. I used a 140 watt gun, trying to minimize heating up the cells.

The Bosch 24 volt battery case is a very tight fit. I had to remove some of the tape which I had applied to keep the cells together in order to get the cells into the case.

After assembly, the battery wouldn't charge. A solder joint broke when forcing the cells into the case. After re-soldering that, the battery still didn't seem to charge. The battery charger showed a steady light instead of a blinking one. I put the pack in my drill and it quickly ran down.
Last night I left the battery in the charger, even though the charger didn't indicate that it was charging. This morning the battery seems to have as much oomph as my other good one. After running it a while, and putting it in the charger, the blinking light showed that it was accepting a charge.

There was a learning curve for me. Next one would be lots easier. The first one was not so easy.

Just as I finished the battery transplant, the FEDEX truck showed up with the new Bosch PS41-2A Lithium Ion Impact Driver which I ordered online.

[Dan Karachio]

Me personally, I am just waiting for the day my batteries die so I can justify going to buy a new LI set! Still, that battery trick is interesting. Can you please explain it for the electrically challenged?

[michael case]

Strange coincidence,

Just went through this last evening with my three year old + out-of-warranty Dewalt drill. In the end, I did what I always do - I bought a whole new drill. The only thing different this time is that business being a what it is, I agonized over it longer than usual. Three reasons I always end up getting the whole new kit: 1 - If the other battery went I'd be very upset 2 - If the drill went I'd be very upset 3 - If the charger went I'd be very upset. Now I have a new drill with a three year warranty and two new batteries and a new warrantied charger. Feels right to me.

[Jack Pinkham]

Me personally, I am just waiting for the day my batteries die so I can justify going to buy a new LI set! Still, that battery trick is interesting. Can you please explain it for the electrically challenged?

Cordless drills using ni-cad batteries use multiple 1.2 volt cells. A 24 volt tool uses twenty 1.2 volt sub-c cells. An 18 volt tool uses 15. The cells are connected in series at the factory by spot-welding metal clips from the negative terminal of one cell to the positive terminal of its neighbor and so on.

You can see if a cell is good by measuring the voltage from its positive terminal to its negative terminal. A reading of zero or negative reading means that that cell should not be reused.

When I opened up my Bosch battery there were only 8 good cells.

Harbor Freight sells 18 volt batteries for $10 on sale. That's about $.67 per cell. Most of the online cells were $2.50 or more. It's possible to buy higher amp-hour rated batteries than the HF ones, though.

I removed the batteries from the HF battery pack and separated them into pairs of cells by breaking the spot welds that attach the clips. The pairs of cells are oriented to match the original battery pack. Then the connector clips are soldered onto the batteries.

There is the possibility of creating a short-circuit when assembling the cells, so use care.