Li-ION battery pack capacity; two 6ah packs, different sizes & weights

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videobruce

New Member
Two 6ah (rated) 40v battery packs. One is considerably larger and heaver than the other. Other than that, the larger has a "HP" designation (hi performance) from the seller/importer. The question is; how can two packs, each with the same rating be of such different sizes & weights?
Note these measured weights and the size comparison attachments. BTW; these are all 40v Ryobi branded packs, not no-name Chinese wonders off eBay.
5ah 51 oz
6ah 53.5 oz
6ah HP 70oz (1.99 kg)

8 Ryobi 5ah pack weight.JPG9 Ryobi 6ah pack weight.JPGRyobi 6ah pack weight.pngComparision between 6ah packs bottom view.jpg
 
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And to keep things interesting, Ryobi has just come out with a 7.5ah pack that is the same size as their 6ah HP pack with measured (not by me) weight of 78 oz. which makes sense over the 70 oz of the 6ah HP pack (of the same size).
I tried to get additional details about the makeup of these packs, but they wouldn't/couldn't devolve anything.
2 Ryobi 7.5ah battery op4075a.jpg
 
The two 6ah packs came out in the same year. :rolleyes:

That doesn't explain two 6ah packs, the larger one with a supposed longer run time. Isn't 6ah, 6ah??
 
It's quite simple 3x2=6, as does 2x3=6. As in 2p vs 3p pack. The max current as well as the power output at any current can vary between different cells. There is more to a cell than a V and Ah rating.

One could use 18650, the other 21700 As well.

Search the tool forums, they will know the internal config for the packs.
 
If 6ah isn't 6ah, how about what hour?
Both packs would be rated at 240 watt hour. Then should I ask, isn't 240 w/hr, 240 w/hr? How is one suppose to tell which pack will run longer if they have the same rating? Isn't ah or w/h a "unit of measure"? Being a u 0f m, it's a constant or point of reference, right? Apples vs apples?
 
The AH rating doesn't tell the whole story. You need to know if the peak current will run your ebike. The packs will have current limiters to protect the cells.

A couple of years ago, I tried the 90WH Ryobi from my weedwhacker on a 500w ebike and was able to go 10-12 miles at 12 mph. Encouraged, I picked up the 180WH model for $120 from Home Depot. I found it would reset itseff on the same bike because it must have had a lower peak current limiter. If I stayed off throttle, it was useable.

I made a spring clip to connect to the batteries. I still use them occasionally for short rides when I want to champion cheap ebiking. You can get even cheaper, but not safer, with hoverboard packs.

A year ago, my charger failed so I picked up a new one for $22. Tossed the old one away, and then realized I should have salvaged the battery clip. Oh well.


P1560254.jpg
 
videobruce said:
If 6ah isn't 6ah, how about what hour?
Both packs would be rated at 240 watt hour. Then should I ask, isn't 240 w/hr, 240 w/hr? How is one suppose to tell which pack will run longer if they have the same rating? Isn't ah or w/h a "unit of measure"? Being a u 0f m, it's a constant or point of reference, right? Apples vs apples?
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No. A 6Ah pack just means at some average discharge level you will in theory get 6Ah if you discharge from full to some specific level. Essentially the same story for Wh rating.

So if you change the load, the instantaneous current requirement, the average current requirement the temperature, the rating of the cell will be different for those conditions, and when you alter too far from the baseline conditions you may see a dramatic difference in capacity.

Most electronic devices need a fixed voltage so they use regulation, which means as the voltage drops the current goes up as they require a given power level.

if you use 3p or 2p configuration the specs for the battery of the same voltage and Wh may differ depending on how the runtime requirements differ from the baseline performance of the cells.

it is also good to understand most ebike batteries are not allowed to discharge to the same level as used for the baseline capacity calculation. So the rating on the cell is not going to translate directly to the actual real world capacity of the final battery.

remember a cell can be a battery, but a battery is very often not a cell.
 
I should add, thou I didn't think it was necessary is, these packs are for lawnmowers, not eBikes. The reason I choose this forum, is you guys seem to know these Li-Ion cells far greater then most including ones in the 'tools' forums, specifically mowers (since there is little reason to do so).

I don't know the current draw of the motor in the mower. To complicate things, most of these mowers have a power saving feature, running the motor at a reduced speed until it senses a greater resistance (slowing down of the blade) due to tall and/or wet grass. Unlike others, Ryobi speeds the motor up immediately and slows it back down as fast (which I'm not crazy about).
 
Ya makes no difference for the discussion right now as we are talking about how capacity is specified, and how that relates to real world capacity. Capacity is always best described by Wh, but the true Wh capacity will depend on the load put on the cell and how that relates to its specific specifications. If you look at a few real cell testers like lygte-info.dk you can see or various cells produce different capacity ratings depending on how they are used, and compare cells of the same rated capacity in different operational models. Then you will see there is still a lot of snake-oil in the world like the Watt rating that were used for light-bulbs forever. The truth is no one number ever tells the whole story no matter what you are trying to classify, so manufactures choose the number they can manipulate the most and actually has the least significance on actual performance.
 
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