2Ah vs 4Ah vs 5Ah: Which Battery Size to Buy
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Amp-hours (Ah) measure how much charge a battery holds, so a higher number means longer run time before you need to recharge. A 4Ah or 5Ah pack will run the same tool for roughly twice as long as a 2Ah pack, but it is also bigger and heavier. For light, short jobs such as driving a few screws or hanging a picture, a 2Ah battery is enough and keeps the tool light. For a drill, circular saw or other tool that you use for hours, a 4Ah to 5Ah pack is the more practical choice. Buy 2Ah only when weight and cost matter more than endurance.
The right size depends on the tool you run it in and how you work. This guide explains what the number means, how battery size relates to power and weight, and how six battery packs listed on this site compare. Nobody here has tested these packs; the figures below come from manufacturer specifications, and the explanations are general knowledge of how lithium-ion batteries work.
What Amp-Hours Actually Measure
A battery stores energy, and amp-hours describe that capacity at the pack's voltage. Multiply amp-hours by voltage and you get watt-hours, the real measure of stored energy. Because the cordless systems in this guide run at similar nominal voltage, comparing amp-hours within one brand is a fair shortcut for comparing run time: a 5Ah pack holds more than a 2Ah pack of the same system.
Amp-hours do not measure power. Power depends on the tool's motor and on how well the battery can deliver current. A small 2Ah pack can run a tool at full speed, but it may heat up faster or run down sooner under a heavy load. Larger packs generally have more cells in parallel, which lets them share the load, so they often stay cooler under heavy use. That is a general principle; check the manufacturer's page for the specifics of any pack.
Voltage Is Not the Same as Capacity
Each pack is tied to a platform: the DeWalt 20V MAX 5Ah Battery 2-Pack is for DeWalt 20V MAX tools, the Makita 18V LXT 6.0Ah Battery 2-Pack is for Makita 18V LXT, the Craftsman V20 4Ah Battery 2-Pack is for Craftsman V20 tools, and the RYOBI 18V ONE+ 4Ah Battery is for RYOBI 18V ONE+ tools. The Milwaukee M18 REDLITHIUM XC5.0 Battery is an 18-volt pack for Milwaukee M18 tools, and the Metabo HPT 18V 2.0Ah Battery 4-Pack is for 18V Metabo HPT tools. Voltage is set by the platform, not by the amp-hour rating, and you cannot move a pack from one brand to another. Choose the capacity only within the system you already own or plan to buy into.
The Size Trade-Off: Run Time, Weight and Cost
2Ah packs
Two-amp-hour packs are the lightest and, per pack, the cheapest. The Metabo HPT 18V 2.0Ah Battery 4-Pack includes four slide-type 18V packs, each 2.0Ah and weighing 0.84 lbs, with a fuel gauge on each. Metabo HPT states 30% longer run time than its BSL1815X 1.5Ah battery. Four small packs are a good fit if you rotate batteries while others charge, or you use light tools such as a compact drill or a brad nailer. It is in the $100–200 price tier.
4Ah packs
Four-amp-hour packs are the middle ground. The Craftsman V20 4Ah Battery 2-Pack is two 4Ah lithium-ion batteries with three LED state-of-charge indicators. The specifications note high-energy cells, no memory effect and virtually no self-discharge. It is in the $100–200 price tier, and charger is not included. The RYOBI 18V ONE+ 4Ah Battery is a single 4.0Ah pack for the RYOBI 18V ONE+ system.
5Ah and 6Ah packs
Larger packs are for long-running work such as circular saws, reciprocating saws, grinders and any day-long use. The DeWalt 20V MAX 5Ah Battery 2-Pack is two 5Ah batteries, each with an LED state-of-charge indicator, backed by a three-year limited warranty. It is in the $200+ price tier. The Milwaukee M18 REDLITHIUM XC5.0 Battery is a 5.0 Ah extended-capacity pack, and Milwaukee lists it as compatible with the M18 system. The Makita 18V LXT 6.0Ah Battery 2-Pack holds 6.0Ah per pack, charges fully in 55 minutes or less, and Makita lists operation down to -4°F, which matters for winter work. The specifications note it is not compatible with non-Star Protection tools.
Comparison Table
| Pack | System | Capacity | Pack contents | Price tier |
|---|---|---|---|---|
| Metabo HPT 2.0Ah 4-Pack | Metabo HPT 18V | 2.0Ah (0.84 lbs each) | Four batteries | $100–200 |
| Craftsman V20 4Ah 2-Pack | Craftsman V20 | 4Ah | Two batteries | $100–200 |
| RYOBI 18V ONE+ 4Ah | RYOBI 18V ONE+ | 4.0Ah | One battery | – |
| DeWalt 20V MAX 5Ah 2-Pack | DeWalt 20V MAX | 5Ah | Two batteries | $200+ |
| Milwaukee M18 XC5.0 | Milwaukee M18 | 5.0Ah | One battery | – |
| Makita 18V LXT 6.0Ah 2-Pack | Makita 18V LXT | 6.0Ah | Two batteries | – |
Price tiers are not directly comparable because the packs hold different counts. A two-pack and a four-pack cost differently per battery, so divide by the number of packs before you compare.
Which Size Suits Which Tool
- Drills and impact drivers. Both 2Ah and 4Ah work. Compact kits often come with 2Ah to keep the tool light; step up to 4Ah if you drive many screws or drill big holes.
- Circular saws, reciprocating saws and grinders. These pull heavy current, so 4Ah to 6Ah is the better match. Our circular saw category shows the options.
- Nailers. Brad nailers use little power per shot, so a 2Ah pack does well, and the lighter pack reduces fatigue when working overhead.
- Outdoor tools. Mowers, blowers and trimmers run for long periods, so the largest pack you can afford is usually the best match.
Weight and Balance in Practice
Weight is the cost of capacity. A larger pack adds weight to a drill or nailer at the end of your arm, and on an overhead task the difference adds up quickly. The specifications give one useful weight point: 0.84 lbs for each 2.0Ah Metabo HPT pack. Not every maker publishes a weight per battery, so check the figure for the pack you are considering. The general pattern is that a larger pack is noticeably heavier.
A good habit is to match pack size to the job rather than to the tool. Many people keep a pair of small packs for overhead and precision work and a pair of large packs for saws and long sessions. Within a platform packs are generally interchangeable, but check the tool's page first: Makita, for example, limits its 6.0Ah pack to Star Protection tools.
Buying Tips
- Start with the system. The platform you already own decides which packs fit. For an overview of kit options, see bare tool vs kit.
- Own two batteries. One in the tool and one on the charger removes waiting.
- Do not over-buy for light work. A big pack makes a small tool front-heavy.
- Check the charger. Several packs, such as the DeWalt, Makita, Craftsman and Metabo HPT multi-packs, are batteries only with no charger included.
- Mind the weather. Cold reduces run time in any lithium pack. Makita specifically mentions winter use for its 6.0Ah pack.
FAQ
Can I use a 5Ah battery in a tool that came with a 2Ah battery?
Generally yes, within the same platform, but check the tool's page first, since a maker can limit a pack to certain tools. The tool will run longer, but it will be a little heavier.
Is a bigger battery more powerful?
Not by itself. A bigger pack lasts longer and may hold up better under heavy load, but the tool's motor decides its maximum output.
Do all brands use the same battery?
No. Each brand has its own connection, and each manufacturer notes that packs work only with their own system.
How many batteries should I buy?
Two is a sensible minimum for regular use. Add more if you use cordless tools all day.