Find out how long your battery takes to charge
Enter your battery and how you charge it, and get the time with solar panels, while driving or on mains hook-up.
Your battery
Description
The battery and the range you want to recharge, for example from 20 % to 100 %. It is used to measure how many amp-hours (Ah) need to be put back.
How you charge it
Description
The charging sources you have. Fill in only yours and leave the rest blank. Panels are measured in watts (W); the alternator charger and the mains charger, in amps (A).
Charging time
Description
How long each source takes on its own to put the charge back, assuming you use nothing in the meantime.
You have changed some data. Press Calculate to update the result.
To understand it better
Worked example
To take a 100 Ah lithium battery from 20 % to 100 % you need to put back 82.5 Ah. With 200 W of panels in spring that is 1.8 days of sun; with a 30 A alternator charger, 2.7 h of driving.
Common mistakes
- Assuming the battery charges well while driving without an alternator charger. In modern vehicles, the alternator alone barely charges a leisure battery.
- Adding up daylight hours instead of peak sun hours: a 200 W panel does not give 200 W all day.
- Using a lead-acid charger with a lithium battery without checking that it has a lithium charging profile.
Questions about this tool
How long do I have to drive to charge the battery?
It depends on the alternator charger. A 30 A unit puts back about 30 Ah per hour of driving, so a half-empty 100 Ah battery needs close to two hours.
Can I charge from panels and by driving at the same time?
Yes. The two sources add up, as long as the total does not exceed the maximum charging current your battery accepts.
Do panels charge on cloudy days?
Yes, but much less: under thick cloud they may give roughly 10 % to 25 % of normal.