Explainers
Milwaukee M18 batteries explained: CP, XC, HIGH OUTPUT and FORGE
CP, XC, HIGH OUTPUT, FORGE: what is the difference, and will each one fit your M18 tools?
Quick picks
The models this page uses as examples.
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Milwaukee M18 REDLITHIUM FORGE XC8.0 battery (48-11-1881)
FORGE tier, 8 Ah*, PWR 4*
- Battery size: 8.0 Ah*
- Milwaukee power level: PWR 4*
- Weight: 2.5 lb
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Milwaukee M18 REDLITHIUM HIGH OUTPUT XC6.0 battery (48-11-1865)
HIGH OUTPUT tier, 6 Ah*, PWR 3*
- Battery size: 6.0 Ah*
- Milwaukee power level: PWR 3*
- Weight: 1.5 lb
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Milwaukee M18 XC5.0 Resistant battery, 2-pack (48-11-1850R)
Two XC packs with a resistant housing
- Battery size: 5.0 Ah
- Weight: 3.4 lb
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Milwaukee M18 XC5.0 starter kit: 2 batteries and M12/M18 charger (48-59-1850)
Two XC5.0 packs plus an M12/M18 charger
- Battery size: 5.0 Ah
- Weight: 4.7 lb
Figures are as stated in each product's current Amazon listing; * from the maker's own spec page (see Sources). Yes or No: whether the listing or maker names the feature.
On this page
What we compared and why
- Battery type. CP, XC and HD describe the size class of the pack, from small to large. Milwaukee describes them in terms of portability and the balance of power and run-time.
- Technology tier. REDLITHIUM, HIGH OUTPUT and FORGE are tiers that Milwaukee says differ in power, heat and charging.
- Amp-hours. The number after the letters, such as the 6.0 in XC6.0, is the amp-hours Milwaukee uses for run-time. It is separate from the tier and the power level.
- The tool and charger you own. Milwaukee says M18 batteries fit M18 tools. Whether you get a stated charge time depends on the charger.
The models compared
| Model | Battery size | Milwaukee power level | Weight | Amazon link |
|---|---|---|---|---|
| Milwaukee M18 REDLITHIUM FORGE XC8.0 battery (48-11-1881) | 8.0 Ah* | PWR 4* | 2.5 lb | See on Amazon |
| Milwaukee M18 REDLITHIUM HIGH OUTPUT XC6.0 battery (48-11-1865) | 6.0 Ah* | PWR 3* | 1.5 lb | See on Amazon |
| Milwaukee M18 XC5.0 Resistant battery, 2-pack (48-11-1850R) | 5.0 Ah | Not stated in listing | 3.4 lb | See on Amazon |
| Milwaukee M18 XC5.0 starter kit: 2 batteries and M12/M18 charger (48-59-1850) | 5.0 Ah | Not stated in listing | 4.7 lb | See on Amazon |
Read at this page's build and converted to one unit by us; sources as in the key above. "Not stated in listing": the listing does not give it. "Listing gives two values": it states two, so we show neither.
Milwaukee M18 REDLITHIUM FORGE XC8.0 battery (48-11-1881)
Why it is here: Power-hungry M18 tools, if you also have or plan to get a charger that supports COOL-CYCLE; Milwaukee gives it PWR 4 and its top charging claim on this page.
Skip it if: Your tools are drills and drivers for light jobs; the extra power and the charger pairing are aimed at heavier work.
Milwaukee M18 REDLITHIUM HIGH OUTPUT XC6.0 battery (48-11-1865)
Why it is here: An XC-size pack with more power than a plain XC, which is the direct answer to high output vs XC: Milwaukee states 50% more power and 50% cooler running.
Skip it if: You want the FORGE tier's charging claims; this is one tier below it.
Milwaukee M18 XC5.0 Resistant battery, 2-pack (48-11-1850R)
Why it is here: Workshop or garage use around oils and greases; Milwaukee describes this XC pack's housing as resistant to them. The listing weight is for two packs.
Skip it if: You want the power of HIGH OUTPUT; this is a standard-tier XC pack.
Milwaukee M18 XC5.0 starter kit: 2 batteries and M12/M18 charger (48-59-1850)
Why it is here: You have M18 tools sold as tool only, and no battery or charger; the listing names two XC5.0 packs and a charger for both M12 and M18.
Skip it if: You already own an M18 charger; a battery alone adds less to your shelf.
The short answer
XC is a size. HIGH OUTPUT is a tier. So "HIGH OUTPUT vs XC" compares two different things: a HIGH OUTPUT XC6.0 is an XC-class pack in the HIGH OUTPUT tier, and Milwaukee says it delivers 50% more power and runs 50% cooler than a standard M18 XC pack. FORGE is the next tier, which Milwaukee promises has the most power, fastest charging and longest life within REDLITHIUM. All of them are M18 batteries, and Milwaukee says M18 batteries fit M18 tools. This page is research-based, from Milwaukee's own pages and the current listings; we have not used these batteries.
How to read the label
Take "M18 REDLITHIUM HIGH OUTPUT XC6.0":
| Part of the name | What it tells you | Here |
|---|---|---|
| System | Which tools it fits | M18 |
| Tier | Power, heat, charging | HIGH OUTPUT |
| Type | Size class | XC |
| Number | Amp-hours, which Milwaukee ties to run-time | 6.0 Ah |
Plain "M18 REDLITHIUM XC5.0" has the standard tier. "M18 REDLITHIUM FORGE XC8.0" has the FORGE tier and a larger Ah number.
Size class: CP, XC and HD
Milwaukee's battery guide describes the three types like this, in order of size.
| Type | Milwaukee's description | Milwaukee says it suits |
|---|---|---|
| CP (Compact) | Most portable, small and lightweight, less power and run-time | Smaller tools, lighter jobs, overhead work, tight spaces |
| XC (Extended Capacity) | Most versatile, mid-level size and weight, a balance of power and run-time | Jobs needing more power and run-time without a heavy pack |
| HD (High Demand) | Most powerful, largest size and weight, most power and run-time | Power-hungry jobs that need uninterrupted work |
No CP pack was available from a genuine Milwaukee listing we could confirm at the time of writing, so the examples above are XC packs. The CP row still applies if you find one; check that the listing is Milwaukee's own and not a third-party replacement.
Tier: REDLITHIUM, HIGH OUTPUT and FORGE
Milwaukee treats REDLITHIUM as the baseline. HIGH OUTPUT, it says, delivers 50% more power and runs 50% cooler than earlier packs. FORGE promises the most power, fastest charging and longest life. Milwaukee's guide also says FORGE is currently only available in the M18 and MX FUEL systems.
Power level is not run-time
Newer packaging carries a PWR number, where a higher number means a higher power level. Milwaukee's own examples show why the Ah number and the PWR number have to be read separately:
| Battery | PWR level | Amp-hours |
|---|---|---|
| HIGH OUTPUT XC6.0 | 3 | 6 Ah |
| FORGE XC6.0 | 4 | 6 Ah |
| HIGH OUTPUT HD12.0 | 4 | 12 Ah |
| FORGE XC8.0 | 4 | 8 Ah |
Read the table across: the two XC6.0 packs share an Ah figure but not a power level, and the HIGH OUTPUT HD12.0 and the FORGE XC6.0 share a power level but not an Ah figure. Milwaukee states directly that power level and run-time are not directly related, and it says it has only begun categorizing its batteries this way, so not every pack has a number yet. Milwaukee also says the FORGE XC8.0 gives the power of a HIGH OUTPUT 12.0 in a pack 20% smaller and 30% lighter.
What fits what
| You own | Fits an M18 tool? | Fits an M12 tool? |
|---|---|---|
| Any M18 battery: CP, XC, HD, HIGH OUTPUT, FORGE | Yes, per Milwaukee: "M18 tools = M18 REDLITHIUM batteries" | No. Milwaukee says batteries are not interchangeable across systems |
| An M12 battery | No | Yes, within its own system |
For the choice between those two systems, see Milwaukee M12 or M18. Milwaukee's own pages give different tool counts for the M18 system, from 150+ to 300+, depending on the page and its date. The compatibility statement is the part to rely on, not the count.
Charging is the one place a pairing matters. Milwaukee ties the FORGE XC8.0's stated 35 minutes to 80% to one charger, the M18 Dual Bay Simultaneous Super Charger (48-59-1815), and says its COOL-CYCLE cooling needs a capable charger. An older charger is not ruled out by anything we read, but do not expect those figures from it. Check the battery's page for your charger.
Which label fits the job
- Light, overhead or tight-space work, mostly drilling and driving: a CP pack, by Milwaukee's description.
- One battery across most tools: an XC pack. If you already have plain XC and your saws or grinders feel limited by the pack, HIGH OUTPUT is the step Milwaukee describes for that.
- Heavy tools, and you will pair it with the right charger: FORGE.
- You have tools and no battery: a battery and charger kit such as the 48-59-1850. See bare tool or kit.
For reading volts and Ah on any maker's tools, see the cordless tool spec sheet explained.
Reading the table
Figures with a mark come from Milwaukee's pages, linked under Sources. Other cells come from the current listing. Listing weights may include packaging, and on the 2-pack and the kit they cover more than one item, so they are not a pack-to-pack comparison. "Not stated in listing" under power level means we did not find one stated for that pack.
What this page does not tell you
We have not used these batteries and make no claim about runtime on a given tool. The percentage claims are Milwaukee's own, against its own batteries; we have not measured them. Milwaukee's pages are the authority and can change as new packs are released.
Sources
- Milwaukee: How to choose a REDLITHIUM battery, with types, tiers and power levels (onekeyresources.milwaukeetool.com)
- Milwaukee M18 HIGH OUTPUT XC6.0 battery 48-11-1865 product page (milwaukeetool.com)
- Milwaukee M18 FORGE XC8.0 battery 48-11-1881 product page (milwaukeetool.com)
- Milwaukee M18 XC5.0 Resistant battery 48-11-1850R product page (milwaukeetool.com)
- Milwaukee press release on the M18 FORGE line (milwaukeetool.com)