What is a battery exactly?

A battery – short for accumulator – is a rechargeable power source. It stores energy and releases it when needed, e.g., to power electric motors. Nowadays, almost exclusively Lithium-ion batteries are used in tools – and we will focus precisely on these in this blog.

Why Lithium-ion? Advantages over older battery types

Earlier battery generations, such as Nickel-Metal Hydride (NiMH) or Nickel-Cadmium (NiCd), suffered from overheating, memory effect, short lifespan, and high weight. In contrast, Lithium-ion batteries are:

• compact & lightweight
• charge resistant without memory effect
• high capacity with high voltage
• robust against typical loads during use

What do 10.8V, 12V, 18V and 20V mean?

These specifications represent the voltage – i.e., the “power” of the battery. The following applies:

• 10.8V = 12V: The nominal voltage (10.8V) describes the average value, the 12V the maximum charge state.
• 18V = 20V: Same principle, just higher dimensioned. 20V sounds more powerful, but is the marketing counterpart to 18V.

The systems are usually compatible within one manufacturer. It depends on the actual voltage and suitable design.

Battery lifespan – Which models suit whom?

• Professionals: High-quality batteries with high capacity & fast charging capability
• Hobby DIYers: Mid-range batteries with solid performance for regular use
• Occasional users: Standard models – inexpensive, but sufficient for simple tasks

Rule of thumb: The more frequently and intensively you use batteries, the more an investment in quality pays off.

Fast charging, energy output & load

Powerful chargers and power-intensive tools like saws strain batteries significantly more than, for example, a cordless drill. High current flows stress the cells and shorten their lifespan. Therefore, plan the usage in advance and choose the battery & charger according to the intended use.

Permanent wear and tear from storage – what you need to know

Unused batteries also age – due to so-called basic wear and tear. Charged batteries lose 3–5% capacity per month – even without use.

Storage tip: Charge batteries to 50–60% for longer storage time – this minimizes cell stress and protects against deep discharge.

Temperature and batteries – the right handling

• Storage: 5–15 °C – cool, but frost-free
• Working: -10 °C to +55 °C – standard range for modern battery packs

Avoid extreme heat or direct sunlight. And: Do not store in a cold car!

Cell connection: Series vs. parallel connection

Series connection: Voltage increases, capacity remains the same.
Example: 9 cells x 2 V = 18 V at 5 Ah

Parallel connection: Voltage remains, capacity increases.
Example: 9 cells x 5 Ah = 45 Ah at 2 V

Important: Only combine cells with the same values and preferably from the same manufacturer.

Watt-hours as a comparison value

To truly compare batteries, the following applies:

Wh = Ah × V → Watt-hours (Wh) indicate how much energy a battery can deliver per hour.

Example: 4.0 Ah × 18 V = 72 Wh