Which connection of lead-acid batteries increases system capacity?

• A. In series
• B. In parallel
• C. In series-parallel
• D. In parallel with a step-up converter

Answer: (B)

Capacity in a lead-acid system is the amount of charge available at a given voltage, usually expressed as amp-hours. When batteries are wired in parallel, their capacities add while the voltage stays the same. So two identical 12-volt, 100-amp-hour batteries in parallel give you a 12-volt bank with 200 amp-hours of capacity, meaning a given 12-volt load can run about twice as long.

If you wire batteries in series, the voltage doubles (to 24 volts) but the capacity in amp-hours stays the same, so the runtime at the original voltage isn’t increased unless you use a converter or redesign the system. A series-parallel arrangement can raise both voltage and capacity, but for simply increasing runtime at the same voltage, parallel is the straightforward method. Using a parallel connection with a step-up converter doesn’t create more energy; it just changes voltage, with efficiency losses.