zero4199

This is related to heated ski boots but I figured the RC community is the best place to go.

My wife has heated ski boots and one set of batteries will no longer take a charge. The charger is a USB that splits into two for both sets of boots. its a simple looking, very small device that turns from red to green once the batteries are charged
I measured 4.14v on the set of batteries that still work. I cannot get batteries from the manufacturer or dealer.

I ordered a set of batteries from Amazon. I can't show a picture until I have 10 posts. DC 3.7v 2600mAh 9.62Wh 505573

Can I wire them in parallel, after checking voltage is similar, stick them back in her boots and not fear burning up her leg?

Thanks
Mike

ticedoff8

My comment is "no".
Without know more details of the Amazon batteries, having a voltage of 3.7 implies they are a Lithium chemistry - maybe a Lithium Ion (LiIon).
And, you really don't know what the proper voltage is for the boots, even though one shows 4.1v

But, I'd be willing to bet that the boots use a NiCad or NiMH 4-cell pack and not Lithium cells. A healthy 4-cell NiCad / NiMH would read 4.8v at full charge and a weak one might read 4.1v fresh off a 24hr charge.

While a Lithium pack at 3.7v may not cause the boot to catch fire while she is wearing them, charging them improperly may. Besides, I doubt that 3.7v would be enough to warm the heaters enough to notice.
And, the boot probably doesn't have a Low Voltage Cutoff to detect when the batteries enter their "danger zone". This is not a big deal for NiCad / NiMH, but discharging below 80% of its rated capacity is terminal for a Lithium cell.
Also, if the Amazon cells are a Lithium cell rated for 2600mAh, why would you need to wire multiple cells in parallel? Do you think the original batteries that were in the boots were rated for a higher capacity?

zero4199

the original batteries are 2 batteries wired together. 2 per boot.
they do not say what type of battery they are. they look like Lipo. no individual cylinder cells.
I just took a layer of plastic off and it is stamped underneath "763448AL1300mAh 4.81Wh 20170201 3.7v"

I'm assuming there are 2 in parallel to keep the boots warm for a longer period of time.

ticedoff8

The important parts are these - 1300mAh 4.81Wh 3.7v.
The Date code is 20170201 (made in 01/02/2017)
3.7v implies a LiIon, not a LiPo.
But, if it looks more like a pouch than a cell, it's more likely a LiPo.
And 4.8Wh is basically a 1C discharge rate (1.2A @ 3.7v for 1h).
Either could be rated at 1.3Ah and that's kind of an off the shelf LiIon (but LiIon are typically cell-shaped)
And if there are 2 of these in the boot, they are each 1S. If they are in parallel (like you suspect), then it is a 1S2P.

I don't know how big the opening in the boot is, but I'd start with a 1S1P LiIon (maybe an 18500 cell) rated for 2000mAh (or so) and see if the boot warms up the way you expect it to. If the temp of the boot is okay, then running two (1S2P) will give you 50% longer run time for the heater.
Plus, the LiIon cells are more tolerant to abuse (physically and electrically)

But, if a 1S LiIon cell doesn't reach a decent boot temp, then I try a 1S LiPo rated at 3000mA and see how that works out.
The worst case is that the 1S LiPo (4.2v) burns out the heater. After that, it's "just a boot" instead of a "heated boot".

Propworn

My Feedback: (3)

What stops you from discharging the cell below the recommended low limit. Most dedicated systems like this have a cut off circuitry either built into the unit or the battery pack. It will shut down before the batteries are damaged. Problem is they are single purpose circuits for a particular battery. Substitute the battery type or chemistry and the circuit may not work as designed.

Joseph Frost

Most interesting, never heard of heated ski boots, brilliant idea. LOL. Just curious, where are actually both batteries fitted in the boot and how does it work? Is it just the soul heated with some wire elements or the whole boot is wired up?
Heated ski gloves would be another great idea, just a thought.