I know there is a formula out there for working out the sze of battery to use or for working out how long a battery will last without main's if anyone knows it can you enlighten me please.

I know there is a formula out there for working out the sze of battery to use or for working out how long a battery will last without main's if anyone knows it can you enlighten me please.

er ?

battery capacity divide by current drawn divide by hours,

but to comply with EN you do the sums backwards to get max current available ie a 7amp battery will limit the panel current to 575ma

http://www.riscogroup.co.uk/dynamicPage.aspx?id=87

Typical battery calculator that can be adpted for your requirements, (note the recommended discharge of a VRSLA battery is capacity divided 20 hour duration, a factor should allso be taken into account for the effect of ageing)

The minimum capacity of valve regulated lead acid batteries should be calculated in accordance with the following formula:

Cmin = 1.25 (T1 I1 + D I2/2)

where

Cmin = minimum capacity of the battery when new at the 20 h discharge rate and at 20