# How long will my battery last under this load and with this source?

I need to calculate how long my battery will last until it is completely discharged. I have a load that will draw 154 uA at 1.8 V for a power of 277.2 mW. Assuming that this is running indefinitely how long will it be until my battery dies? The battery has a nominal voltage of 1.2 V and a rated capacity of 2300 mAh.

I also need to take into consideration that the battery is being charged by a solar panel. Assuming 5 hours of sunlight, and an output power of 93.5 mW from the solar panel.

I found that it would take about 56 days. But this seems really long. Should I just take the battery energy and divide it by how much energy the solar panel give per day?

• You state a load which requires 1.8V, but a battery which has a nominal 1.2V P.D. Is there a fundamental problem with your scenario here? – Brian J Hoskins Feb 3 '15 at 10:07
• I am questioning whether your panel output is realistic. Are you using a MPPT solar charger? Perhaps it would be more realistic to use a specific charge current rather than a charge power level. Can you provide a link to the solar panel datasheet? Or if you have it, put it in the sun and measure the short circuit current with an ammeter? – mkeith Feb 3 '15 at 18:52

Well, first of all, I assume there is a mistake and it's 154mA instead 154uA.

Next, assuming no loses in voltage convertion from 1.2v to 1.8v, you will be discharging the battery at 231mAh. With your 2300mAh battery it would take around 10 hours.

Now the solar panel thing. With 93.5mW you are charging the battery at 78mA for 5h, so 16mAh in terms of day opperation. It would take around 143 hours to charge the battery.

• 2300mAh/190mA=~12hours, not days..? – Wesley Lee Mar 6 '15 at 0:21
• Wow, you are totally right. I just said days. My bad. Thank you. – zapeitor Mar 6 '15 at 8:19
• Just out of curiosity: How did you calculate the conversion of 154mA to 190mAh? – Golo Roden Mar 6 '15 at 8:29
• Good question, because it's 231 mAh isn't it? Around 10h then. I wonder what I was thinking about taht day -.- – zapeitor Mar 6 '15 at 9:57