What is C-Rating? When rating the capacity of a VRLA battery, it would have been very acceptable if we could say with a 100Ah battery that you could draw 100A for one hour or 1 A for 100 hours.
However, with a new VRLA battery, pre-charged, this is NOT the case.
The reason for this is the delivery of the energy from a chemical reaction. Therefore, the faster one draws the current, the shorter the time over which this current will be delivered.
A German scientist, notably Mr Wilhelm Peukert, observed this, and an alternative arrangement of expressing capacity has now been formalised, or what is known as the ‘C-rating’.
When purchasing a VRLA (Valve Regulated Lead Acid) battery, the user will note that the battery will display an Amp-hour to a ‘C-rating’.
C-rating describes how much current the battery will deliver over the set time period. Being 20 hours for C20, 10 hours for C10 and 5 hours for C5.
So, for example, the Valen Topin 12V40Ah battery’s C20 rating is 43.4Ah, C10 is 41Ah and C5 is 38.3Ah.
In these expressions, the letter ‘C’ is more easily understood if you think of it as simply the Hours at which this battery is rated.
You can use the battery’s stated capacity and the C-rating of the battery to calculate how many amps it can constantly discharge until it’s fully discharged.
For example, if you take a 100Ah battery and divide it by its C-rating, C10, you get 10A or 10 amps. So this battery can discharge 10A for 10 hours until it is fully discharged.
For the same battery, the stated battery capacity varies per C-rate. The faster the battery is discharged, the smaller the stated capacity is.
Designing a system and specifying the size of the battery
With the battery capacity varying depending on the rate at which the current is drawn, the specification battery size for an installation can be tricky.
Over-sizing the battery is desirable, but physical space and a tight budget may not allow this. The specification sheet of each of the Valen batteries provides an indication of the capacity at different rates of discharge. A more exhaustive study is available in the Valen Battery Specification Manual.
It is worth noting that when comparing batteries, make sure that the C-Ratings are the same, so you have a true comparison.
Do you have more technical questions on batteries?
If you have any questions regarding an upcoming project or past battery system, the Valen team are here to support you. With customer service being one of our core values, we go above and beyond for our clients.