There are various way to do this, none of which are risk-free. Any damage to you, your personal property, nature, the Universe is entirely your fault.
You Cannot Fully Charge Your Device
The bottom line however is that you should avoid fully-charging the battery. Instead you should aim for a short charge, giving you enough juice to continue operating your device for a limited time period. In other words the solution outlined below is a temporary fix which is aimed at giving you time to get to the nearest (safe) power supply.
You will need:
- A power supply of some sort
- Something to use as a resistance to reduce the current flow between your charger and the battery
- Light bulbs are perfect for this kind of thing
- Protective gear of any kind
- Loose wiring to connect things together
- Basic knowledge of electronics.
There is a guide I found here which explains both the underlying method and the safety risks involved. To summarise:
- Check your power supply output - both Voltage
Vs and Current
- Check your battery specs - Voltage rating
Vb and maximum charge in mAh
- Compute the potential difference
ΔV = Vs - Vb between your supply and battery
Once you have this data you use Ohm's law
V = Ic * R to compute the resistance you need to obtain enough current to charge your battery, but low enough for this procedure to be safe
Ic << Ib
- This computation would work out to something like this:
Ic = ΔV / R where
R = Sum(r) is the total resistance provided by whatever you are using as a resistor
- If you are using bulbs as resistors you would have to measure their resistance, either empirically like the guy in the link I posted did, or mathematically using again Ohm's law (see this as an example calculation)
- The resistors must be placed in series so that their total resistance is equal to the sum of the individual resistances
At this point you wire the resistances in series
- Wear protective clothing: gloves and glasses are a minimum!
- You then connect the negative pole of the power supply
S to the negative pole of the battery
-S -------- -B
- To charge you now have to connect the positive pole of the power supply
S to the bulbs, to the positive pole of the battery
+S ---- Sum(r) ---- +B
How do you know if this is working? The battery temperature will increase.
Based on your previous computation, since you know the mAh rating of the battery you know how long you have to apply current
Ic for it to be fully charged. Also know that the typical charge profile of a battery is not linear, so applying current for half the time required for a full charge will not half-charge your battery. It will most probably charge it more.