If your cordless drill dies halfway through a job that it used to finish with juice to spare, you've got a battery that won't hold charge. It's the most common complaint I hear on site, and the fix isn't always "buy a new one." Sometimes it's a 20-minute job a working electrician can walk you through. Here's how I test, clean, and—when it actually makes sense—revive a pack instead of throwing money at a new battery.
Why a Battery Suddenly Won't Hold a Charge
Before we touch anything, understand the three usual culprits:
- Corroded or dirty terminals — the pack has plenty of life left, but power can't flow out cleanly.
- A dead or unbalanced cell group — one weak cell drags the whole pack down.
- Reaching the end of its cycle life — after 500–1,000 charge cycles, capacity naturally sags.
Most guys jump straight to "replace it." That's wrong at least half the time. Start cheap, work your way up.
What You'll Need
- A multimeter (digital, nothing fancy)
- Isopropyl alcohol (90%+) and a soft brush or old toothbrush
- A clean rag and fine sandpaper (400-grit or finer)
- A screwdriver set and plastic pry tool, in case the shell needs opening
- Protective gloves and safety glasses — lithium packs deserve respect
Step 1 — Rule Out the Charger First
I can't count how many "dead batteries" I've seen resurrected by just swapping chargers. Try the suspect pack on a different charger if you have one, and try a known-good pack on the same charger. If a different battery charges and runs fine, the problem is the charger, not the pack. A battery that won't hold charge and a battery that simply never charges are different problems — get this straight before you open anything.
⚠️ Common mistake: Blaming the battery when the charger or the tool's contacts are the real issue. Always isolate the variable first.
Step 2 — Clean the Terminals
Corrosion is sneaky. A pack can look fine and still have a chalky film on the contacts that kills the connection. Pop the battery off the tool, look at the metal prongs, and if you see any whitish or greenish buildup, here's the fix:
- Wipe the terminals with isopropyl alcohol and a soft brush.
- For stubborn spots, gently polish with fine sandpaper — light touch, don't strip the plating.
- Wipe clean and dry before reinstalling.
Do the same on the tool's contacts and the charger's contacts. Dirt here reads as "won't hold charge" to a novice, and it's the cheapest fix on this list.
Step 3 — Test the Pack with a Multimeter
Now we find out if it's a connection issue or a cell issue. Set your multimeter to DC volts and touch the probes to the pack's big positive and negative terminals (usually labeled + and −, sometimes behind the mounting rails).
- 18V / 20V Max pack reading ~19–20V: Cells are holding voltage just fine. The problem is almost certainly connection or a worn-out pack that can't deliver current under load.
- Reading below ~15V on a fully charged pack: You've likely got a weak or dead cell group dragging everything down.
This reading tells you whether reviving is worth it. If the pack reads full voltage but still dies fast in the tool, we move to the next step.
⚠️ Risk warning: Opening a lithium pack means handling 40–50V DC across the cell block. Shorting it with a metal blade across the wrong two cells will flash and arc. Work slowly, on a non-conductive surface, and never pierce a cell.
Step 4 — Balance Revival (When the Cells Are Just Drifting)
If your multimeter shows one cell group consistently below the others, that imbalance is why the pack won't hold charge — the protector cuts off early to save the weak cell. In many DIY-friendly packs (especially aftermarket ones), you can nudge things back:
- Open the shell with a pry tool, being careful not to flex the cell block.
- Note the cell groups and their voltages. A group of 3.6V cells should sit around 3.7–4.0V.
- Charge the low group individually to match the others (a balance charger that handles li-ion in 1S/2S steps handles this cleanly).
- Close the pack, charge fully, and re-test.
This is genuinely a judgment call. If one cell group is severely low (below 2.5V) or swollen, do not try to revive it — replacing a pack is cheaper and safer than a swollen-cell gamble. When the pack is truly past its useful life, grab a fresh Dewalt DCB203 replacement battery or the equivalent for your platform instead of fighting the old one.
Step 5 — Check the Tool's Contacts and Brush Wear
A battery that won't hold charge in one specific tool but works fine in another is a tool problem. On brushed tools, worn brushes draw more current, heat up the pack, and make it cut out early — which feels exactly like a dying battery. Clean the tool's terminals (same alcohol trick from Step 2) and, if the tool is an older brushed model, check the brush condition. Replacing a $10 pair of brushes can make a "dead" battery feel new again.
Step 6 — Reset the Pack's Low-Voltage Cutoff (the Last Resort)
Some packs trip their internal protection circuit when they sit dead too long, and they refuse to charge until that circuit resets. The safe DIY version:
- Put the pack on the charger for 30–60 seconds.
- Remove it, test voltage on the terminals.
- Repeat once or twice.
- If the charger still shows nothing, the protection board may need a reset.
Strong warning: Don't fall for the old "jump the positive and negative with a chunk of wire to wake it up" trick you see on YouTube. On bare cells it can work; past the protection board it's a dead short and an arcing, sparking, battery-ruining mistake. If a gentle charge-and-test cycle doesn't wake it, retire the pack.
Common Mistakes to Avoid
- Skipping the charger test. You'll buy a $60 battery to fix a $20 charger problem. Test everything else first.
- Cleaning only the battery, not the tool and charger contacts. Dirt lives on both ends of the circuit.
- Opening a pack without checking the voltage first. You don't know what you're dealing with until you measure.
- Fighting a swollen or deeply discharged cell. If a cell is puffed or sits below ~2.5V, it's done. Reviving it is a fire risk, not a cost saver.
- Assuming "won't hold charge" always means "dead." Every pack on my bench that "just dies" has at least a 30% chance of being a dirty contact or a tired tool.
Frequently Asked Questions
Why does my power tool battery work but won't hold a charge very long?
Usually it's cell imbalance or the pack nearing end-of-life. Step 3's voltage test tells you which. If cells read healthy but runtime is short, you're fighting reduced cycle capacity — time for a replacement.
Can a dead battery that won't hold charge be fixed for good?
Sometimes. Terminal cleaning and balance revival can buy real extra life. But a pack that's hit its cycle count won't be restored by cleaning — it's genuinely worn out.
Is it safe to take apart a lithium power tool battery?
Only if you know what you're doing and you've tested it first. If you're uncomfortable around exposed lithium cells, stop at Step 2 and let a professional or a fresh pack handle it.
How do I stop this from happening in the first place?
Don't store packs fully drained, keep them at partial charge in a cool spot when idle, and follow our how to extend your battery's lifespan guide — good charging and storage habits are what keep a pack holding charge for years instead of months.
The Bottom Line
A power tool battery that won't hold charge is frustrating, but it's not automatically a dead battery. Test the charger, clean every contact, measure the pack, and only then decide whether revival or replacement is the honest call. Nine times out of ten on my bench, the fix is cheaper than a new battery — and when it's not, at least you know you earned the replacement instead of guessing.