The REDARC BCDC1220 is a 12/24 Volt 20 Amp under bonnet DC to DC battery charger designed to keep your battery charged whilst driving. Featuring multi stage battery charging, the system charges your auxiliary battery from your vehicle to a proven 100%.**large capacity battery banks may require a few cycles to fully charge.The BCDC charger will work from a wide operating range (9 – 32V) giving the option of charging from both 12V and 24V vehicle systems, and is potted and rugged making it perfect for under bonnet installations.By providing a unique charging profile to each specific battery type, the smart charger is able to achieve and maintain 100% charge for your auxiliary battery. You can charge your auxiliary battery no matter what your battery is.