Watt Hrs vs Amp Hrs
This article helps explain these ratings and raises a question wrt battery charging older vs newer LFPs too. Not sure if this also applies to other battery types or if it matters with any when you me...
Forum Discussion
If you are sticking purely with 12vDC devices, amp-hr is fine for most uses. Technically batteries don't stay exactly at 12v but for most uses, it's close enough.
If you are changing voltages or to AC, watt-hr makes more sense. Otherwise, it's critical to specify X amps @ Y volts.
But for heaven's sake, don't say I used 20 amps or 5000 watts yesterday and need to replace them in my battery bank or worse 20amp/hr.
- The first is an instantaneous measure of output. Without knowing how long you were drawing of the batteries, you have no clue how much was used.
- The second is the rate of change in output (ie: I started drawing 10amps but over an hour it gradually rose to 30amps, so the rate of change is 20amp/hr) Largely a nonsense figure as most electrical loads do not change at a steady rate.
If you are changing voltages or to AC, watt-hr makes more sense. Otherwise, it's critical to specify X amps @ Y volts.
But for heaven's sake, don't say I used 20 amps or 5000 watts yesterday and need to replace them in my battery bank or worse 20amp/hr.
- The first is an instantaneous measure of output. Without knowing how long you were drawing of the batteries, you have no clue how much was used.
- The second is the rate of change in output (ie: I started drawing 10amps but over an hour it gradually rose to 30amps, so the rate of change is 20amp/hr) Largely a nonsense figure as most electrical loads do not change at a steady rate.
