Power Tool Batteries: How They Work, How to Make Them Last

Your manual wins. These are general practices. When your tool's manual says something different, follow the manual.

Volts and amp-hours, in plain words

• Volts (V) are the push. More volts means more power for the tool. 18V and "20V MAX" packs are the same class: 18V is the nominal rating and 20V is the peak with no load.
• Amp-hours (Ah) are the size of the tank. A 5.0Ah pack runs roughly twice as long as a 2.0Ah pack on the same tool.
• High-output packs (for example Milwaukee HIGH OUTPUT, DeWalt POWERSTACK and FLEXVOLT, Makita XGT 40V, Ryobi HP) deliver more current. Saws, grinders and mowers run cooler and stronger on them.

Match the pack to the tool

Charging rules

• Let a hot pack cool before charging. Most chargers wait automatically, so a "hot pack" light is normal.
• Don't charge below freezing. Lithium-ion packs can be damaged when charged cold. Bring them inside first.
• Use the brand's own charger. Off-brand chargers skip the communication that protects the cells.

Storage

• Store packs partly charged (about half) if they will sit for weeks.
• Keep them out of a hot truck cab or bed in summer. Heat ages cells faster than use does.
• Keep loose packs away from metal (screws, coins) that can bridge the terminals.

Knockoffs and adapters

• Cheap "compatible" packs often skip the cell balancing and temperature protection real packs have. They can fail early or catch fire.
• Cross-brand adapters void the warranty on both sides and remove protections the tool expects. If you mix platforms, keep separate packs for each.

Signs a pack is done

• Runtime drops by half or more.
• The charger flashes a fault on more than one charger.
• The case is swollen, cracked, or smells like burning plastic. Stop using it.

Disposal

Take dead lithium-ion packs to a battery drop-off (many Home Depot and Lowe's stores take them through Call2Recycle). Tape the terminals first. Never put them in the trash.