When subjected to extended periods of non-use or low temperatures, diesel engines are often difficult to start. Maxwell Technologies now offers a 24-volt ultracapacitor-based Engine Start Module (ESM), claimed to be ideal for improving equipment uptime and power reliability in industrial vehicles with diesel engines. Unlike batteries, which produce and store energy by means of a chemical reaction, ultracapacitors store energy in an electric field. This electrostatic energy storage mechanism enables ultracapacitors to charge and discharge in as little as fractions of a second, perform normally over a broad temperature range, operate reliably in up to 1 million or more charge/discharge cycles and resist shock and vibration. The ESM completely takes over the engine cranking and starting function by remaining fully charged, even if battery voltage drops significantly. There are two models of the 24-volt ESM: The ULTRA 31/900/24V for starting diesel engines up to 12.5 liters and the ULTRA 31/1100/24V for engines up to 15 liters. Both are packaged in BCI Group 31 form factor.