How many watts to charge a li-ion battery

solomon_says

If my battery is rated at 2200 mAh, how do I estimate how many watts I expect to use recharging it? I also have a dc adapter.

mvas

Does your battery have a voltage rating?
Do you know what the formula is for Watts?

solomon_says

Oops. Its 12V. I don't know how to calculate watts from mAh's

mike95490

Li-Ion is pretty efficient.  If you use 342watts, 350watts would recharge it pretty close to full again.
 But to figure out a solar charger for it, you better stick to about 90% of battery capacity, to use for your solar harvest guesstimate.

2.2Ah x 12V = 26 watt hours in that battery.  So a 50w panel, with average placement (25w output) could charge it in an hour.
 Unless its too late tonight and I'm not doing the math right

Estragon

The battery is pretty efficient, but the DC adapter (aka wall wart) may not be. You may be able to make a guess on this by looking at in input and output values printed on it.

For example (made up values), say it's 0.5a @ 120vAC input, and 2a @ 12vDC output. That would be 0.5x120=60w in, which is the rate of power use. If it takes two hours to charge, total energy used is 120w.

2x12=24w is going to the battery. The difference, 60-24w = 36w is going to heat the wall wart. Also, some wall warts can use power just being plugged in. I put mine on a power bar which gets turned off when not in use.