Tale of two batteries (HF AGM 17AH vs Ebay AGM 18AH)

[DSchmidt_2000]

Bought one of the Harbor Freight jump starter packs to keep in the car. Just a blow molded case with a 17AH AGM battery inside, high current switch, jumper cables and charger built in.

Also bought an 18AH AGM battery off ebay for fiddling, which when it arrived had USA stamped on the case and the seller confirms was made in the USA.

Decided to see how true their ratings were using my CBA II. Current load was 7amps.

17AH HF battery measured out at 10.32 AH at 7A load


18AH Ebay battery measured out at 15.17Ah at 7A load


Quite a difference.

[MrWizard]

yeah but that peak is only for micro-seconds
they never tell you how they reached that Peak rating,
i suspect by measuring a direct short "spike" and not a consistent load of an automobile starter

[DSchmidt_2000]

Thanks everyone. Mainly I wanted to show the performance difference between an HF 17AH pack and a domestically made 18AH battery. I knew about the 20hr rating being at a much lower current draw, but would have expected these two to measure close and if anything the 17AH pack, meant for a jump pack, to have lower internal resistance/higher AH's delivered under the same load.

wa8yxm wrote:
Also: Batteries are designed differently depending on their intended use. Those jump packs are designed to provide very very very high current, 17 Amp Hours sounds like about a 750 to 900 amp peak pack.

Looking around Amazon, I see puny little 12V 7AH batteries in the 750-900A peak jump packs. This one for instance.

Review


This one likely has a 18AH'ish pack inside and is '1700' peak amp.
That's marketing for you.

[wa8yxm]

As I often say: THe faster you discharge the battery the faster*Faster it runs down (Thanks Mena for the spelling) thanks to Mr. Puekert (I can never remember ho to spell that).

What you have done is prove his findings.

Try amp hours/20 for the current load and see how the batteries do.

Also: Batteries are designed differently depending on their intended use. Those jump packs are designed to provide very very very high current, 17 Amp Hours sounds like about a 750 to 900 amp peak pack.

A "Deep cycle" design may not be able to provide that kind of current. But you can suck a larger precentage of the charge before bad things happen.

GOOD analyzer though.

[mena661]

MrWizard wrote:
Yes it is, but 7 amps is a heavy load for such a small battery
The std twenty hour test , for a battery that size would have been about 800 milliamps

X2 Mr. Puekert would take more amps out of the battery with heavier loads.

[MrWizard]

Yes it is, but 7 amps is a heavy load for such a small battery
The std twenty hour test , for a battery that size would have been about 800 milliamps