Alt text: picture of a Costco mechanical fish (cat) toy taken apart.
I had one of these fail last night from the battery lead coming off as pictured. That is something I expected. Upon opening the mechanism, both sides of the lithium cell have very concerning damage in a piercing type of abrasion. The cell is relatively small.
Speculatively, I expect the stuffed toy is flammable, making this an ideal house fire starter if the cell gets bridged layers in the battery from a puncture and goes into a runaway state.
All it needs is a way to secure the battery with some double sided tape and extra insurance like some kind of soft filler fabric or material to stop it from rattling around. Maybe add a bit of hot glue to the battery leads at the circuit board to insure they do not fail from a lack of strain relief.
I haven't retraced the circuit, but the battery looks fine otherwise. It appears to have a DW01 like protection board at the cell, and a 4054 batman according to the silkscreen.
This is a serious issue that should not be ignored.
how powerfull is this thing that regular batteries weren't enough?
A normal AA battery is probably more powerful than this tiny thing. That cell is probably 3.7v 250 mah at best. My “shitty” ikea rechargeable AAs are like 900 mah, and the good ones are 2400 at 1.2V. 3.7 * 250 is 925 watt hours, 1.2* 900 is 1000, and 1.2 * 2400 is 2800.
The biggest benefit is these are easily and quickly rechargeable.
An alkaline AA may have more capacity, but the LiPo has lower internal resistance and it's electrolyte is flammable. The worst the alkaline would do it shorted or punctured is get warm and poop out KOH.