Update- 11 Oct 20, Update 2- 12 Oct 20 Thinking one 100AH battery that can be drawn down to very low SOC gives you nearly the same "usable AH" as two regular AGM or Wet batts, as seen advertized, is bogus ?What about Peukert? If you pick a steady amp draw like 5 amps, then that is the 20 hr rate for the 100AH batt, but is only half the 20 hr rate for the two 100s. So you would get way longer time at 5 amps with the two 100AH batts.It is bogus to advertize that you get nearly the same AH because you can draw the one batt down so low but the other two are limited to 50% SOC using good practice. That is only because you are comparing 5 amps with 10 amps for the draw.A "usable AH" is a clever invention indeed. :(

I'm thinking your logic is BiasedLithium 100ah use 80ampHrs reach 20% SOCRecharge do it again tomorrowAgm or FLA 200 amp hrs, use 80 amp hrs Draw down to 60% SOCRecharge do it again tomorrowWhich battery/bank is going to suffer the most degradation, which is going to give more hours, days, years of service,Which will need the lesser amount of generator run time to recharge the same 80 amp hrsYour statements above are only correct, If you plan draw them to zero SOC full discharge total output, and throw them away,

You need to compare the actual peukert function for each battery. As the internal resistance drops there is much lower effect due to high load. Also peukert is an exponential curve. Much lower effect at anything less than the 20 hour rate.

MrWizard wrote:I'm thinking your logic is BiasedLithium 100ah use 80ampHrs reach 20% SOCRecharge do it again tomorrowAgm or FLA 200 amp hrs, use 80 amp hrs Draw down to 60% SOCRecharge do it again tomorrowWhich battery/bank is going to suffer the most degradation, which is going to give more hours, days, years of service,Which will need the lesser amount of generator run time to recharge the same 80 amp hrsYour statements above are only correct, If you plan draw them to zero SOC full discharge total output, and throw them away,My only thought was that the 80AHs are not the same running time at 5 amps. At 5 amps from the 100AH batt, that is 16 hours time. 5 amps from a 200AH bank would be a longer running time.If your "use" is a 5 amp draw, then your "usable time" (vs a "usable AH") is more with the two batts.IMO you have to do the same activity or "use" , which is the same amps draw, to make the "usable" comparison.

Useable aka Safe for the battery in question,Is not the same as Total Storage drain it empty

OK he specifically ask what about Peukert.The Peukert effect is something I do not see commented on enough. What is it?Well take that 100 AH battery. Put a 5 amp load on it and it in 10 hours it is down to 50%.... (100/20=)But what happens if we put a 10 amp load on it? Does it hit 50% in 5 hours? (Double the amps half the time?) NO it hits 50% in closer to 3 hours.. Exactly how fast I do not know. This is what the Peukert effect is. The faster you draw amps the faster^2 the battery runs down. And no I do not know how much faster it runs down.. May vary with battery type.

Battery Draw Bogus Math? Peukert UPDATE 2 | Good Sam Community

34 Replies

MrWizard
Moderator
Oct 09, 2020
Useable aka Safe for the battery in question,
Is not the same as Total Storage drain it empty
BFL13
Explorer II
Oct 09, 2020
MrWizard wrote:
I'm thinking your logic is Biased

Lithium 100ah use 80ampHrs reach 20% SOC
Recharge do it again tomorrow

Agm or FLA 200 amp hrs, use 80 amp hrs
Draw down to 60% SOC

Recharge do it again tomorrow

Which battery/bank is going to suffer the most degradation, which is going to give more hours, days, years of service,
Which will need the lesser amount of generator run time to recharge the same 80 amp hrs

Your statements above are only correct, If you plan draw them to zero SOC full discharge total output, and throw them away,

My only thought was that the 80AHs are not the same running time at 5 amps. At 5 amps from the 100AH batt, that is 16 hours time.

5 amps from a 200AH bank would be a longer running time.

If your "use" is a 5 amp draw, then your "usable time" (vs a "usable AH") is more with the two batts.

IMO you have to do the same activity or "use" , which is the same amps draw, to make the "usable" comparison.
time2roll
Nomad
Oct 09, 2020
You need to compare the actual peukert function for each battery. As the internal resistance drops there is much lower effect due to high load. Also peukert is an exponential curve. Much lower effect at anything less than the 20 hour rate.
MrWizard
Moderator
Oct 09, 2020
I'm thinking your logic is Biased

Lithium 100ah use 80ampHrs reach 20% SOC
Recharge do it again tomorrow

Agm or FLA 200 amp hrs, use 80 amp hrs
Draw down to 60% SOC

Recharge do it again tomorrow

Which battery/bank is going to suffer the most degradation, which is going to give more hours, days, years of service,
Which will need the lesser amount of generator run time to recharge the same 80 amp hrs

Your statements above are only correct, If you plan draw them to zero SOC full discharge total output, and throw them away,

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Battery Draw Bogus Math? Peukert UPDATE 2

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