**Peukert Law, Batteries, and You**

Time for another STICKY THREAD. This is more bad news for you off-grid battery folks. Peuket law is like Death and Taxes, you will pay, and for 99% of you a lot more than you have too. Peukert Law simply states for flooded lead acid batteries: "

*The higher the discharge rate (Amps) the less capacity the battery actually has*". For example your 100 amp hour battery can be as low as 30 AH if discharged at the 1 hour discharge rate of 100 amps. Or as high as 160 AH at the 100 hour rate of 1 amp.

In theory only with batteries:

Amp Hours = Amps x Hours

Hours = Amp Hours /Amps

Amps = Amp Hours / Hours.

Well that theory only applies at the discharge rate the manufacture specifies the battery at which is typically 20 hour rate. So for example if you have a a 100 AH battery the 20 hour rate is 5 amps 5 amps = 100 Amp Hours / 20 Hours). From that formula a layman would assume if you had a 100 AH battery you should be able do discharge that battery at 1 amp for 100 hours, or 1 hour at 100 amps. YOu would be wrong, very

**WRONG**, Mr Peukert will not allow it. If you were to discharge that 100 AH battery at 1 amp Mr. Peukert smiles and will makes your battery a 133 AH battery meaning you can discharge it for 133 hours at 1 amp. On the other hand if you were to discharge it at 100 amps or the 1 hour rate Mr. Peukert frowns and robs you with only allowing you 30 AH or a mere 18 minutes when you expected 60 minutes. Surprise!

Here is Mr Peukert in real terms a Rolls 30H125. It is a 125 AH 12 volt battery. Look at the Discharge Rate table. At 100 hours it is a 166 AH battery. At 1 hour it is a 45 AH battery.

To make life simple over the years I and other battery professionals have come up with a generic Peuket derating Correction Factor called

**C**. It can be used to ball park determine or adjust if you will for your actual discharge rate where True Amp Hours = C x Rated AH @ 20 hour rate. To bget actual numbers will have to come from the specific battery manufacture and model number. But this will get you close for preliminary design.

1 Hour = .3

2 Hour = .5

3 hour = .6

4 hour = .65

5 hour = .7

6 hour = .75

8 hour = .8

10 hour = .85

12 hour = .9

16 hour = .95

20 hour = 1

24 hour = 1.05

36 hour = 1.1

72 hour = 1.25

100 hour = 1.30

So for example if you have a 100 AH battery and discharge at the 2 hour rate (50 amps), then 100 AH x .5 = 50 AH.

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