Do powerpack/jump starters have the power they claim ?

[Justin Smith]

1 hour ago, alexp999 said:

It won’t be anywhere near 12.5V for most of those Ah though. You have to factor in the voltage drop as it discharges. 

I agree the voltage drops as a battery discharges, the average voltage on the GE2000 I tested was only about 11.2.

Surely the average voltage on a car lead acid battery to discharge (at constant load) would be over 12 though ?

 

[alanfp]

On 6/30/2023 at 10:41 PM, iantt said:

Noco good for jump starting but if used as a powerbank  it's not so good. Only used it as a power bank a few times to charge up a few smartphones while sat in the back of a transit van for 48 hrs with no usb ports. Managed 3 phones before it was flat.

Sounds about right...

A typical smartphone has a battery capacity of under 4,000 mAh. Therefore, a power bank with a 10,000 mAh capacity (real capacity 6,000–7,000 mAh) can charge the majority of smartphones at least two times to 100% capacity.

[alexp999]

1 hour ago, Justin Smith said:

I agree the voltage drops as a battery discharges, the average voltage on the GE2000 I tested was only about 11.2.

Surely the average voltage on a car lead acid battery to discharge (at constant load) would be over 12 though ?

 

12V is the nominal voltage, it’s roughly when a lead acid battery is at 50% capacity, so it’s best to use 12V as the average. 

[Justin Smith]

1 hour ago, alanfp said:

Sounds about right...

A typical smartphone has a battery capacity of under 4,000 mAh. Therefore, a power bank with a 10,000 mAh capacity (real capacity 6,000–7,000 mAh) can charge the majority of smartphones at least two times to 100% capacity.

Surely any quoted figures of (just) mAh are a bit meaningless unless the voltage is also quoted ?
The Eneloop AA NiMh batteries I use are 1900mAh, but at only 1.2V (nominal) that's "only" about 2.3watt hours.
That said 2.3 watt hours for one AA NiMh makes the tested 19 watt hours of my "power bank" pretty poor I'd have thought. That's only equal to about 8 x AA NiMhs ! And they're "only" 1900mAh Eneloops*, larger capacity NiMh AAs are available, 2500mAh for instance that's 20% larger.
If my calculations are correct I could build my own power bank with more power than that with 10 of them, and I'd be able to use the batteries for other stuff as well.

But, be that as it may, a "power bank" only being able to recharge a smart phone twice doesn't sound that powerful to me !

 

* which, in my experience, might have less power but hold their capacity better over the years.

[alanfp]

10 hours ago, Justin Smith said:

If my calculations are correct I could build my own power bank with more power than that with 10 of them, and I'd be able to use the batteries for other stuff as well.

Yes, I think you could - come back when you've done that and let us know how long it took you and post a photo of it. 

[Justin Smith]

7 hours ago, alanfp said:

Yes, I think you could - come back when you've done that and let us know how long it took you and post a photo of it. 

I have been thinking about this. The problem is two fold.

1 - The battery holders I have used before aren't that well made.
Quite frequently there'll be no power coming out because one (or more) of the cells has a poor fit.

2 - One would need the sockets......
The 12V unregulated socket wouldn't be such a problem, but USB sockets (with regulated outputs) would be rather more of an issue. Plus, if one wants to have 12V croc clips (for jump starting) that's more complication !

[Justin Smith]

I sent the Gooloo GE2000 back and instead have bought a "VORSPRUNG" powerbank off amazon for £70, this one. It claims 81 watt hours capacity but on test I only got about 39 watt hours out of it : 3hrs 10min at an average 14.6 volts into 17 Ohms.
That's just under half its specified capacity but still about twice that of the GooLoo GE2000.

Its 12V output is actually about 15V (actually a max of 16.4V down to 13.2V just before the unit went flat).

Does anyone know if my Uniross battery charger, or other units specified for a 12V input, will work OK with no damage at that voltage ?