In this guide
Ah stands for amp-hours. It is the size of a battery's fuel tank: a 5.0 Ah pack holds about two and a half times the charge of a 2.0 Ah pack at the same voltage, so the tool runs about two and a half times longer between charges.
Key points:
- Ah measures capacity (runtime), not voltage and not speed.
- More Ah means longer runtime, but also a bigger, heavier and more expensive pack.
- Voltage × amp-hours = watt-hours (Wh), the fairest way to compare packs across 12V and 18V platforms.
- On high-draw tools, a larger high-output pack can also deliver more power, because it holds voltage better under load.
What Ah means on a tool battery
An amp-hour is one amp of current delivered for one hour. A 5.0 Ah battery can in theory supply 5 amps for one hour, or 10 amps for half an hour. Real runtime depends on how hard the tool is working, the temperature and the age of the pack, so treat Ah as a way to compare packs, not as a clock.
The number is printed on every pack. On Milwaukee batteries it is also in the name: CP2.0 is 2.0 Ah, XC5.0 is 5.0 Ah, and so on.
1.5 Ah, 2.0 Ah, 3.0 Ah, 5.0 Ah, 6.0 Ah, 8.0 Ah: what each size is for
| Capacity | Energy on an 18V pack | Best for | Trade-off |
|---|---|---|---|
| 1.5 to 2.0 Ah | 27 to 36 Wh | Drills and impact drivers on light work, overhead work, tight spaces | Shortest runtime; not suited to saws and grinders |
| 3.0 to 4.0 Ah | 54 to 72 Wh | All-day drilling and driving with moderate weight | Middle ground on runtime and weight |
| 5.0 to 6.0 Ah | 90 to 108 Wh | The everyday pack for most trades: hammer drills, impact wrenches, band saws, reciprocating saws | Noticeably heavier on a compact tool |
| 8.0 Ah and up | 144 Wh and up | High-draw tools: grinders, circular saws, rotary hammers, press tools used all day | Heaviest and most expensive; longer charge time |
Watt-hours in the table are simply volts × amp-hours using the 18V nominal rating (for example 18 × 5.0 = 90 Wh).
Does a higher Ah battery make the tool more powerful?
Ah by itself is capacity, not power. But larger packs usually have more cells, or larger cells, sharing the load, so voltage sags less when the tool pulls a lot of current. On a drill driving screws you will not feel a difference. On a grinder, circular saw or rotary hammer, a high-output 6.0 or 8.0 Ah pack can keep the tool from bogging down where a 2.0 Ah pack would.
Ah vs. volts vs. watt-hours
- Volts (V) set the platform: 12V tools take 12V packs, 18V tools take 18V packs. You cannot mix them.
- Amp-hours (Ah) are capacity within a platform.
- Watt-hours (Wh) are total energy: volts × amp-hours. A 12V 4.0 Ah pack stores 48 Wh; an 18V 4.0 Ah pack stores 72 Wh, so the same Ah number does not mean the same runtime across platforms.
For more on voltage platforms, see how to choose a power tool battery and how to read power tool specs.
Which Ah should you buy?
| Tool | Sensible pack size |
|---|---|
| Drill/driver, impact driver, 12V installation tools | 2.0 to 4.0 Ah |
| Hammer drill, impact wrench, band saw, reciprocating saw | 5.0 to 6.0 Ah |
| Grinder, circular saw, rotary hammer, press tool, vacuum | 6.0 to 8.0 Ah high-output or larger |
A common setup is two 5.0 Ah packs for general work plus one larger high-output pack for the tools that drain batteries fastest.
Battery packs in stock at Tool Mart
| Battery | Platform | Capacity | Price |
|---|---|---|---|
| Milwaukee M12 REDLITHIUM CP2.0 (48-11-2420) | 12V | 2.0 Ah | See price |
| Milwaukee M12 REDLITHIUM XC 4.0 | 12V | 4.0 Ah | See price |
| Milwaukee M18 REDLITHIUM XC5.0 (48-11-1850) | 18V | 5.0 Ah | See price |
| Milwaukee M18 REDLITHIUM HIGH OUTPUT XC6.0 (48-11-1865) | 18V | 6.0 Ah | See price |
| Milwaukee M18 REDLITHIUM HIGH OUTPUT XC8.0 | 18V | 8.0 Ah | See price |
See all power tool batteries and chargers.
Where to buy power tool batteries in Houston and San Antonio
Tool Mart stocks power tool batteries at both Texas stores, open Monday to Friday, 7:30 AM to 5:00 PM. Order online for same-day pickup or call the counter to check stock before you drive over.
- Houston area: 13721 S. Gessner #200, Missouri City, TX 77489 · 713-222-8665
- San Antonio: 10568 Sentinel St, San Antonio, TX 78217 · 210-655-6116
Outside Houston and San Antonio? We ship by UPS Ground and freight: browse batteries and chargers.
Frequently asked questions
What does 5.0 Ah mean on a battery?
It means the pack stores 5 amp-hours of charge: enough to supply 5 amps for about an hour, or less current for proportionally longer. On an 18V platform that is 90 watt-hours of energy.
What does 1.5 Ah mean?
1.5 amp-hours, a compact pack. It is light and fine for a drill or impact driver on short tasks, but it drains quickly on saws and grinders.
Can I use a higher Ah battery in my tool?
Yes, as long as it is the same brand and voltage platform. A higher Ah pack will not damage the tool; it just runs longer and weighs more.
Does a higher Ah battery take longer to charge?
On the same charger, yes: there is more capacity to refill. Rapid chargers shorten the wait for large packs.
Is a 6.0 Ah battery better than a 5.0 Ah battery?
It holds 20% more charge. Whether it is better depends on the tool: for saws, grinders and rotary hammers the extra capacity and output help; on a compact drill you may prefer the lighter pack.
Order online for same-day pickup at either store, or call the counter and we will check stock for you.
Tool Mart has sold professional tools to Texas contractors since 1976, with stores in Houston and San Antonio.