How to Choose the Right Replacement Battery
Learn what specs matter, what to avoid, and how to find an exact match for your device.
The Most Important Rule: Match the Specs, Not Just the Name
When your battery dies, the temptation is to search "[device name] battery" and buy the first result. That works sometimes — and fails expensively other times. Here's how to get it right every time.
The Three Numbers That Matter
Every battery has three specs that determine compatibility. All three must match (or be compatible with) your original battery:
Voltage (V) — This must match exactly. A 10.8V device needs a 10.8V battery. Using higher voltage can damage your device. Using lower voltage means it won't work properly. Common tool battery voltages: 12V, 18V, 20V. Common laptop voltages: 10.8V, 11.1V, 14.4V, 14.8V.
Capacity (mAh) — This is how long your battery lasts per charge. You can safely go higher (e.g., swap a 2,000mAh for a 4,000mAh) — it just means longer runtime. Going lower means shorter runtime. Never go lower than 80% of the original capacity.
Chemistry (Li-ion, NiMH, NiCd) — Most modern devices use Lithium-ion (Li-ion). Older tools use NiCd or NiMH. Do not mix chemistries — the charger for one won't work correctly with another, and in some cases it's a fire risk.
How to Find Your Battery's Specs
Three reliable ways:
1. Look at the battery itself — voltage, mAh, and chemistry are printed on the label of virtually every battery ever made. 2. Check the device manual — the battery specs section lists the OEM part number and specs. 3. Use WhatBatteryFits.com — enter your device model and we'll show you every compatible battery with specs verified.
OEM Part Numbers: Your Best Friend
The OEM part number is the manufacturer's original code for the battery (e.g., DCB205 for a DeWalt 20V battery). If you search for a replacement using the OEM part number, you're guaranteed to find compatible options. This is more reliable than searching by device name.
What to Look for in a Seller
Once you've confirmed the specs, evaluate the seller:
- Seller feedback — on eBay, look for sellers with 98%+ positive feedback and 100+ transactions
- Certifications — look for CE, UL, or RoHS certifications on the listing
- Return policy — reputable sellers offer 30-day returns on batteries
- Avoid — listings with no specs listed, prices that seem impossibly low, or sellers with under 50 feedback
The Bottom Line
Replacing a battery is safe and cost-effective when you match the specs. Voltage must be exact. Capacity can go up. Chemistry must match. Use the OEM part number as your search anchor. Buy from sellers with verified feedback.