Resurect a Dead Rechargeable Shaver

OK so I have an old remmington shaver,the batteries died and since I am both cheap and lazy, I could not possibly throw it out, or expend too much effort on it.

since im exceptionally lazy, and this is a generic repair guide, I wont waste time, explaining how to open your shaver/device. but I will say if it clips together, wedge a credit card inbetween the crack,and slide it at a 45 degree angle.

Alas I digress...anyways apon opening the beast, I find that it contains 2 batteries... err cells, in series, with no smart charging, just 3v in. YIKES. for those unfamiliar with Ni-mh technology....it sucks! These batteries were commonly used during the dark ages

So I bought 10x USB li-ion chargers, a few months ago, on eBay as an impulse buy, they were only 2 dollars... dont judge me.

from what I can remember, from my research, there are 2 main types of cheap USB li-ion charger. one really sucks bad, and the other type...the ones I ordered, aren't great. there main problem, is that they are linear, not "switched". what that actually means, is that charging efficiency could be anywhere between 50-65 percent, depending on input/output voltage difference as apposed to 85-95 percent. but these chargers do have some 'intelligence', where they taper off the voltage, according to the charge status

I managed to salvage 4 of 6 viable li-ion cells from a dead laptop battery(3000mah). I think the general rule of thumb is, if a lithium ion cell is less than 2.45 volts, it is wasted, so throw it away, or recycle, if you are an unwashed hippie. another tip is, if you allow a li-ion cell to drop below 20 percent frequently, it does shorten the workable cell life.

you can salvage li-ion batteries, from old cellphones, broken tablets, and whatever else you can find or you can buy them online, cheap from China, if you are willing to wait a month(banggood,/eBay/tinydeal)

not much to say...when soldering, try to rather solder to tabs, if present. heres the part where I tell you not to do what I usually do...so here goes. dont solder directly onto the terminals, this will transfer the heat directly into the seals,and the insulation, causing leakage or explosions ?.... Having said that, neither have ever happened to me, tho if you do want to try it, make sure you wear safety glasses, file /rough up the smooth metal, so the solder sticks (its a surface area thing) also solder quickly with the highest wattage iron, you can find(60w +)

in retrospect, I probably should have stuck a diode, reverse bias, across the chargers +and-to protect the charger from the voltage spikes, created by the motor!

not much to say again... other than INSULATE every connection, or the battery WILL short, start a fire, or spray liquid hot electrolyte magma into your face, rendering you darth vader-esque

blah blaaa

...well almost....functionally it is better than new, its got mad power! it slices though bone, like cheese... almost. the only downside is that running it for a long time, may cause it to overheat, im not sure what the safe current rating of the motor is

a few further improvements , would be

#1 stick a diode in parallel with the charger, in reverse bias... this will protect the charger from an effect known as C.E.M.F (google it). the least boring explanation for it, is: when electricity flows through a conductor...or in this case the motors wire coil, a magnetic field will form around said conductor. when you remove the power, the magnetic field Will collapse, or 'deflate' like a balloon, when it cuts into the conductor , a high voltage(100s to1000s of volts) will be created ('induced') in the conductor destroying anything connected to it

to counter this effect we install diodes , to act as a dead short, to dissipate the surge. that blueish/green...err...aquamarine? arrow thingy is the symbol for a diode. it acts as an 'electronic non-return valve", only allowing electricity one way

Another thing we could do is install a 3 pole , 2 position switch, in such a way that , when OFF, the battery is connected to the charger only, when ON the battery is disconnected from the charger, and connected to the motor. batteries don't seem to mind quick high voltage spikes, from my experience.... unless they have built-in discharge protection circuitry (like any li ion battery with 3 terminals). which reminds me ....another ominous warning....li ion batteries can dump all their charge into a load in a matter of seconds, if they don't have protection circuitry, and are abused. this will lead to rapid heating, and possible fire/ battery pop-page and molten siff tasting mildly toxic electrolyte being sprayed everywhere. do research before doing this.

Anyhoe I digress, NC stands for Normally Closed, meaning, when you haven't touched the switch that closed is those contacts normal condition is closed = on, conducting or 'continuous').
likewise, NO stands for: Normally Open, normall condition of those contacts is open=off , or open circuit

I hope this has been helpful.
and remember children,caution,knowledge and common sense increases survivability by 95 percent