Watt-Hours (Wh)
Affiliate link — we may earn a commissionWatt-hours combine voltage and amp-hours into a single energy number. The formula is simple: voltage times amp-hours equals watt-hours. A 20V 5.0Ah battery stores 100 Wh. A 40V 2.5Ah battery also stores 100 Wh. Same total energy, different voltage. Watt-hours are the fairest way to compare batteries across different voltage platforms because they account for both the electrical pressure (voltage) and the tank size (amp-hours). Airlines cap lithium batteries at 100 Wh for carry-on without approval and 160 Wh with airline approval. Most tool batteries fall under 100 Wh.
Why It Matters
When comparing cordless tools across brands or voltage tiers, watt-hours gives you an apples-to-apples energy comparison. A Ryobi 40V 5.0Ah battery (200 Wh) stores more energy than a DeWalt 20V 5.0Ah (100 Wh), even though the amp-hour number is the same.