Introduction
You invested in quality Milwaukee batteries, but lately they don't seem to last as long as they used to. The runtime is shorter, they feel hot after charging, or they're dead when you grab them off the shelf.
Here's the thing: lithium-ion batteries are sophisticated pieces of technology, and treating them like indestructible bricks is a fast track to premature failure. After years of using (and occasionally abusing) Milwaukee batteries, I've learned these lessons the hard way.
Let's talk about the five most common mistakes that are secretly destroying your batteries—and how to fix them.
1. Leaving Batteries in Extreme Temperatures
This is the #1 battery killer, and most people don't realize how sensitive lithium-ion cells are to temperature.
The Problem
In Hot Environments (Above 105°F):
- Accelerates internal chemical degradation
- Can permanently reduce capacity by 20-30% in a single summer
- Increases risk of thermal runaway (rare but dangerous)
In Cold Environments (Below 32°F):
- Dramatically reduces available capacity (temporary)
- Can cause lithium plating during charging (permanent damage)
- Makes batteries appear "dead" even when charged
Where This Happens
Hot:
- Leaving batteries in your truck bed during summer
- Storing in a hot garage or shed
- On a sunny dashboard
- In direct sunlight on a job site
Cold:
- Truck cab overnight in winter
- Unheated garage or shop
- Outdoor storage
The Solution
Storage Best Practices:
- Keep batteries between 40°F and 80°F when possible
- Store indoors during extreme weather
- Use an insulated tool bag if you must leave batteries in vehicle
- Bring batteries inside overnight in winter
Working in Extreme Temps:
- Let cold batteries warm to room temperature before charging
- Rotate batteries between use and a temperature-controlled environment
- Keep spare batteries in an insulated bag or cooler (yes, really)
- In summer, store batteries in the shade
Pro Tip: If a battery feels ice-cold or very hot to touch, let it normalize to room temperature before use or charging. Charging a cold battery is particularly damaging.
Real-World Impact
I tested this with two identical 5.0Ah batteries over one summer. One lived in my temperature-controlled shop. The other stayed in my truck toolbox (regularly hit 130°F+).
After 3 months:
- Shop battery: Normal performance
- Truck battery: Lost approximately 25% capacity, noticeably weaker under load
That $99 battery was effectively damaged $25+ in value in one summer.
2. Storing Batteries at Full or Empty Charge
How you store batteries when they're not in use has a huge impact on lifespan.
The Problem
Storing at 100% Charge:
- Creates high internal stress
- Accelerates capacity fade
- Reduces overall cycle life by 15-25%
Storing at 0% Charge:
- Can lead to deep discharge over time (self-discharge happens even when off)
- May damage battery protection circuits
- Battery can become difficult or impossible to recharge
The Science
Lithium-ion batteries are happiest at a partial state of charge. Full charge puts stress on the cell chemistry, while empty leaves them vulnerable to deep discharge damage over time.
The Solution
For Short-Term Storage (Days to Weeks):
- Any charge level is fine
- Use them as normal
For Long-Term Storage (Months):
- Charge to 40-60% (two or three bars on the fuel gauge)
- Check every 2-3 months and top up if needed
- Store in a cool, dry place
How to Hit 50% Charge:
- Use the battery until the fuel gauge shows 2-3 bars
- Or charge a depleted battery for ~30-40% of normal full-charge time
- Don't stress about perfect precision—anywhere from 40-70% is fine
Real-World Application
If you're a homeowner who uses tools occasionally: After your project, don't leave batteries on the charger until next use. Charge them to about half and store them.
If you're a professional with backup batteries: Rotate your battery stock. Don't let batteries sit fully charged on the shelf for weeks while you use others.
What About Batteries in Tools?
If you leave a battery in a tool for a week, it's fine. But storing a battery in a tool for months? Remove it. Tools have small parasitic drains that can slowly discharge batteries.
3. Always Running Batteries Until They're Completely Dead
You might think fully discharging batteries before recharging is good practice (like old NiCad batteries), but lithium-ion is different.
The Problem
Deep Discharges Stress Lithium-Ion Cells:
- Each deep cycle (0-100%) causes more wear than multiple shallow cycles
- The protection circuit cuts off the battery before true "0%," but running it until the tool stops still counts as a deep cycle
- Repeated deep cycles reduce overall battery life
The Better Approach
Shallow Cycles Are Actually Better:
- Running batteries from 80% to 30% and recharging causes less wear than 100% to 0%
- Lithium-ion has no "memory effect"—you can charge anytime without harm
The Solution
Ideal Usage Pattern:
- Swap batteries before they're completely depleted
- Recharge whenever convenient
- Don't worry about "training" the battery by full discharges
Professional Tip: Keep multiple batteries on hand and rotate them. When one drops to 30-40%, swap it out. This extends life across your entire battery fleet.