Well first you need to know - what capacity has your battery ? (that's the number before the "Ah" - called Ampere-hours) then you need to know how much current you are sucking out of the battery. Just from the number of LED's alone you still don't know how much they draw - You can drive a LED with 1, 10 or even 1000mA. Then it's the question - are they in series or in parallel ? -> easiest way is to measure the current you draw from the battery. Then there's another not so simple question: how much charge does the battery need to still be able to crank the car ? 10% 20% ? 30% ? (we leave the temperature problem out here as it would make it even much more complicated). Example: you have a 50Ah battery fully charged (we assume it has no tolerances...which is impossible...) You draw continuously 1A We assume you need 20% charge to still be able to start the car 50Ah * 20% = 10Ah -> you have 40Ah left for the LEDs. 40Ah / 1A = 40h - > 40 hours. Headlights on: 2*55W / 12V = ~10A 40Ah / 10A = 4 hours and you have to push the car (or even less as I was only calculating the H4 low beams without the rest) just the doors open with bulbs -> 5W/ bulb = 30W/12V = ~3A 40Ah / 3A = ~13h Doors with LED's that draw 20mA each -> 6*20mA = 120mA 40Ah / 120mA = ~300h Hope this helps to calculate your own figures. Elvis & 6548 > I'm trying to figure out how long a fully charged battery will last. > What is the mathmatical formula for doing it? All my lights (except > headlights) are LEDs. The tail & front market lights have 45 diodes, > the side markers have 3 diodes, license plates have 6 diodes, door > markers (assuming I keep the doors open) have 6 diodes. > > So with doors open and parking lights on (headlights off) how long will > my batter last from a full charge? > To address comments privately to the moderating team, please address: moderators@xxxxxxxxxxx For more info on the list, tech articles, cars for sale see www.dmcnews.com To search the archives or view files, log in at http://groups.yahoo.com/group/dmcnews Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/dmcnews/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/dmcnews/join (Yahoo! ID required) <*> To change settings via email: mailto:dmcnews-digest@xxxxxxxxxxxxxxx mailto:dmcnews-fullfeatured@xxxxxxxxxxxxxxx <*> To unsubscribe from this group, send an email to: dmcnews-unsubscribe@xxxxxxxxxxxxxxx <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/