In the corner of some garages there is a drill from the 1990s that is as heavy as a brick and yet remains perfectly straight. The battery and the charger for it are both dead, and whenever the owner thinks about repairing it. Here's whether they should.
The only two practical options are to use an adapter with a new lithium battery in the existing tool or to buy a new tool kit. There is a third possibility, which is to rebuild the battery using new cells, but you should not do that. Above all there is one red line: lithium batteries must never be charged using a NiCad charger.
The following guide carries out the straightforward calculation regarding the switch from NiCad tools to lithium ones: it looks at the different options, the benefits, the three safety rules, and the decision that most other guides omit—that is, when it is not worth saving the old drill. For information on batteries in general, please see our electric tool battery guide.
The two routes: adapter or new kit
The adapter route is well known. DeWalt has an official adapter, the DCA1820, which enables modern 20V MAX batteries to be used with its older 18V stem tools. The battery is placed on the adapter, and the adapter is then inserted into the tool, allowing the old drill to operate using the new battery chemistry. The drawback is that the lithium battery can only be charged in a correct 20V charger and not in the old NiCad charger, and with some of the smaller older tools the smaller packs are required since the larger ones physically interfere with the tool.
What the rebuild route involves is taking apart the pack and replacing the lithium cells. The Power Tool Institute's safety advice is direct in stating that it is by opening the packs to repair them that fires begin, and this guide agrees with that, which is the reason why you are being given the concept rather than a step-by-step tutorial. The question about rebuilding is the one we are asked most often, and the answer in all cases is no; if a pack is no longer working, then replace it, don't use it.
The route involving the new kit is the one that is never discussed and is frequently the correct one.
| Route | What it is | The honest read |
|---|---|---|
| Official adapter | New lithium pack on the old tool | Great if you have several old tools |
| DIY rebuild | Open the pack, swap cells | Not worth the fire risk |
| New kit | A modern drill with fresh batteries | The better buy for one old tool |
What you gain
The maths behind the upgrade are straightforward. Lithium batteries weigh about half as much as an equivalent nickel-cadmium battery, so instead of carrying an extra pound or two on your wrist all day, you don't have to. There's no memory effect, which means you no longer have to carry out the procedure that nickel-cadmium batteries required. The self-discharge rate drops from about 15 to 20 per cent per month with old nickel-cadmium batteries to about 1 to 3 per cent with lithium batteries, which is the reason the nickel-cadmium battery that used to be charged by the old charger was always dead when you needed it. Also, lithium batteries retain their full charge right until nearly empty, whereas nickel-cadmium batteries lost power gradually throughout the discharge process.
Whenever people decide to make the switch, they always mention the weight; it affects the way the tool feels in the hand and is noticeable within the first minute.
The three rules that keep you safe
Three rules, in order of importance.
1. Lithium never charges in a NiCad charger. The chargers function in a different way, and it is this mismatch that causes battery fires to start. All the warnings from various brands are identical. When you buy a set or an adapter, the lithium charger is included in the purchase and not an optional addition.
2. Old tools have no low-voltage protection, so stop when it sags. Modern tools and batteries are able to communicate with one another and switch off before the battery pack is over-discharged. Older NiCad tools aren't like this and most adapters do not include this protection either. The proper procedure is manual: as soon as the tool seems to be tired, you should stop using it and charge it. Keep operating it until it stops, and you might end up permanently damaging the lithium battery pack.
3. Take the battery off the adapter when you're done.Adapters, even the official ones, can cause a slight discharge when they're connected, and users have reported their packs being dead after just a few days of being left on the tool. However, the battery doesn't lose charge when the pack is disconnected. Each month we receive emails about adapter-drain: the pack was full on Friday but dead by Monday. So make it a habit to remove the pack.
The honest math: when the old drill isn't worth saving
This is the option which is left out of most upgrade guides.
It is clear what the benefit of using an adapter is when there are a large number of existing tools available; for instance, if you have three or four old tools and either one adapter or two, the whole collection can then be fitted into modern cases. This procedure is referred to as a fleet upgrade and it is worth carrying out.
If you have only one drill, then using an adapter is just a waste of money. Suppose you take an old drill, attach an adapter, buy a new battery pack and a new charger; in that case you'll have spent money in order to keep going a drill that is twenty years old. Instead, with the same amount of money you could purchase a modern drill kit, which is lighter, stronger and comes with two battery packs and a charger. Even though the old drill was a good one, it still does not constitute a good investment. It is exactly by repairing a cheap tool with expensive parts that people become hoarders.
If your old tools span brands and you're weighing adapters across platforms, the general rules live in our power tool battery compatibility guide. And if the old collection turns out not to be worth saving, you can browse replacement batteries by brand for the modern platform you land on.
Common questions about the NiCad upgrade
Can you convert a NiCad tool to lithium?
Yes, in the practical sense: an adapter like DeWalt's official DCA1820 runs a modern lithium pack on an old 18V stem tool. What you can't do is charge that lithium pack in the old NiCad charger, and you shouldn't rebuild the pack yourself.
Is it worth upgrading NiCad to lithium?
Depends on the fleet. Several old tools, worth it, one adapter wakes them all. One old drill, usually not, because a modern kit costs about the same as the adapter, pack, and charger combined.
Can you charge a lithium battery in a NiCad charger?
Never. The chargers work differently, and charging lithium on a NiCad charger is how battery fires start. A proper lithium charger is part of the upgrade, not an optional extra.
Do battery adapters drain the battery?
Some do, slowly, including official ones, because the connection can trickle a small drain while it sits. The fix is simple: take the battery off the adapter when you're done with the tool.
How do I convert my old drill to lithium?
Buy the adapter route or buy a new kit. Do not open the old pack and swap cells yourself. Pack surgery is how fires start, and the safe answer to a dead pack is a replacement.
The drill in question should not end up with a poor investment. We have several old tools—namely, the adapter, the new charger, and the fleet will come to life. In another scenario, just one old tool should be allowed to retire with dignity and the budget should be used to buy a modern kit. In both cases, lithium will never be charged by the NiCad charger and the pack should never be left on the adapter overnight.
References & Sources
- DeWalt official site (DCA1820 adapter compatibility and charging guidance)
- Power Tool Institute battery safety guidance (Power Tool Institute, the power tool industry's safety association)
Need a replacement?
If the old fleet is being retired, browse replacement batteries by brand. We stock compatible packs for twelve modern platforms, and any question goes to a real person through our contact page.