On Thursday, September 10, 2020 at 4:04:57 PM UTC-4, kinsell wrote:
On 9/10/20 7:55 AM, wrote:
On Thursday, September 10, 2020 at 12:48:52 AM UTC-4, wrote:
The bluetooth feature is a gimmick. What really makes these attractive is that they are about 1/2 the price of equivalent the K2 battery!

Some months ago I bought several "PowerSync" (related to "PowerSonic"?) LFP batteries, the non-smart version (no Bluetooth), for about $32 each, from a US seller on ebay. Rated 7.5 AH, and the same standard "brick" size as the common 7AH SLA batteries. At that price, they are cheaper than SLAs (since they will last at least twice as many years). I cut one open, so I can tell you that (1) the ones sold at that price were 2 years old when sold (date stamped late 2017), not great but no big deal, (2) the cells are the small 18650 size, like the ones used in laptop batteries (but LFP chemistry in this case), and (3) yes it includes a full BMS including cell balancing. I've used them in an electric bicycle and in an electric mower, so I can report they work OK in high-drain use (but the BMS shuts off at about 20 amps). In the glider I prefer the larger 12AH battery, but one of these smaller 7.5AH ones is my standard backup plan.

Note that a "7AH" SLA battery that is 2-3 years old will only give you about 3 AH or so if you don't want to damage it by fully discharging it, and the voltage will be pretty low by then. Tested one of these 7.5 AH LFPs by discharging 6 AH out of it, voltage was still well over 13V. The spec sheet claims they are "designed to work with AGM chargers", so you don't even need a new charger if you switch to them from SLAs, although something like the Imax B6 is better.


Three things wrong with the claim that these are LFP batteries. You
said voltage was well over 13 volts after almost a full discharge, but
real LFP's are 12.8 nominal, with four cells. 12.5 volts near the end
of a discharge cycle would be a lot more believable.

The fact that the cells are 18650 form factor should be a tipoff in itself.

Most importantly, LFP doesn't have the energy density needed to pack
that much power into four small cells.

So what you have is some Li-ion battery mis-branded as being LFP.

-Dave

Not at all. The thing is packed with 20 of these cells (4S 5P configuration), 1500 mAH per 18650 cell is reasonable. LFP is famous for holding the voltage above 13V (for a 4-cell battery) until it's almost empty. I didn't discharge it all the way, only 6AH out of the nameplate 7.5AH. (I didn't care enough about the exact capacity to risk stressing the battery with a full discahrge.) If these cells were really Li-ion then 4S would be around 14.4V nominal and much higher than that when charging. Instead it runs around 13.4-13.6V for most of the charging, as it should for LFP.

I have photos of the innards of this thing if anybody's interested.

And no I'm not affiliated with the seller... In fact I put off buying them for a long time since I didn't like the seller's flippant responses to my technical questions, but eventually I found some info elsewhere online, took the risk, and am happy with what I got.