Observed capacity from Ryobi 40V battery

[Dave9]

^ I meant modern. That is a rare exception, 10-20+ years ago IIRC. Can you list any current, or even last half decade, cordless consumer/contractor grade tools that have 18650, LiFePO4 in them? Even an example, is going to be the small minority.

Most pouch pack (assuming that is what you are referring to in "newer flat style") Li-Ion cells used in consumer devices aren't LiFePO4 either. LiFePO4 is barely ever used in consumer grade products today except for things like vehicles and power (solar) storage where they have to withstand more recharge cycles, being more important than higher power density.

 

[factorytuned2012]

I've been rather suspicious that the ryobi battery (40V, 4AH) which came with the powerhead for my hedge trimmer is not accurately rated. I finally have some clumsy observations.

Yesterday, I used the 40V battery with its digital sine wave inverter (ryobi) to charge a deep cycle battery with a digital, computerized charger. I did this twice. The computerized charger was set to a 5A limit (at 12V) and it captures total mAH delivered into the battery under charge.

[40V batt]->[ryobi sine inverter]->[digital charger]->[12V deep cycle batt]

In both cycles, the charger came up to about 14.9V and began tapering the amperage down to not exceed 15V. So I'll use an average of 14.5V (between 12.5 where it started with the highest current and then 14.9 where it spent a little more time tapering down). This average will throw the calcs off a little, but not so much as to discount my observations.

Charge 1: 4800 mAH at 14.5V = 69.6 WH*
Charge 2: 5400 maH at 14.5V = 78.3WH

*I cut charge 1 a little short, stopping the charger when the inverter started to flash warning, but before the 40V battery actually tapped out. So we'll got with #2.

Assuming that the 40V battery is a 40V battery, and not a 36 (?), it's math looks like this:
78.3WH/40=1.95AH

Ouch.

Maybe it's really a 36 volt cell.

78.3/36=2.175AH

That's still an ouch.

Assuming that there is 10% loss (pretty high) in the inverter, and an additional 10% loss in the charger, for a total of 20% loss, the battery could get a little love here.

1.95/.8=2.43 at 40V
or
2.2/.8=2.75AH at 36V

So, best case, the battery is providing 68% of its rated capacity if it's really a 36V cell, or 60.8% it's rated capacity if it's a 40V.

(note, it's been used probably 10 times now, 2 full discharges and the rest are partial, maybe 50%-75% SOC).

Booooo.

-m

I have 12v tools and the batteries read 10.8