I am wanting to find the best way to continuely charge a 12v 70AH battery. I use this battery to power a water purification system in Africa.
220v power is available but goes out regularly (daily). My question is would a 12v car solar battery charger that puts out 100mAs be a good way to continualy charge a 70 AH battery. This system is on the Equator so I figure about 12 hours of direct sun everyday. The power consumption of the purifier is 14 watts.

Now let’s see if I can remember my electrical math.

Power consumption, 14 watts times the length of operation. If you ran your system for 3 hours that would be 42 watt hours. A watt is amps times volts, so you are pulling about 1.2 amp times 3 hours or 3.6 amp hours.

The solar cell is giving you .1 amp at 12 volts and I’ll bet that is a maximum, full, noontime sun so that will drop off. To make up for your usage, you would need to charge for about 30 hours. 30 X .1 = 3.0 amps.

You could use 4 of them together and increase your charging rate. 10 X .4 = 4.0 amps. If you use enough solar cells, you could run it on solar energy all day and not need a battery except for cloudy days.

Now, this answer is not very scientific but it is a start. One of the other, more learned poster will check me out. You can use your own figures and do the same math to get an approximation.

here is west exas, same as africa without elephanst, there are very poor commnities that have bad water. They are making solar stills and each family can get about 1 gallon a day. There are websites with details. Basically the water in fed into a box with a float stop. The box is covered wit glass. The sun causes the water to evaporate and condense on the glas this at about a 10 deg. slant. This sends the distilled H2o to a container.