521/21 is a high quality battery from Numax. The dimensions of the product are 263 x 172 x 217 mm. You should use the dimensions of your old battery as a guide for your selection. Durable Wet technology for your vehicle The 521/21 has a capacity of 146 Ah. The higher the value, the more electrical charge can be stored in the battery. Wet batteries like the 521/21 are suitable for marine dual use with standard energy needs. They offer reliable performance for marine applications. The technology of this battery supports dual starting and supply requirements in marine environments. You should consider this when buying Before you buy, check that the circuit and polarity of your new battery are identical to the values of the old model. The circuit shows whether the positive pole is on the right or left of the battery. To determine this, position the battery so that the poles are facing you. With the 521/21, the circuit is 0, so the positive pole is on the right.