Solar not charging your battery? Check these 7 things

Check these, in order

The quickest fixes come first. Most "not charging" problems end at step 1, 2 or 3.

1. Is the battery already full?

A full battery takes almost no current, so the controller shows very little going in. That's normal, not a fault. Run something for a while and watch whether charging picks back up.

2. Are the panels making enough voltage?

A charge controller only starts charging when the panels make about 5 volts more than the battery, and keeps going while they stay at least 1 volt above it. A 12V battery sitting at 13 volts needs about 18 volts from the panels just to start.

Night, clouds, shade, dirt and the low winter sun all cut this. So does a small array: if one panel barely clears the battery's voltage, it may never start in weak light. Check the panel and battery voltage in the controller's app or display, or with a meter at the controller's terminals.

3. Is a lithium battery too cold?

LiFePO4 batteries can't charge below freezing (32°F / 0°C). Their battery management system (BMS) blocks charging until they warm up, and some systems stop around 41°F (5°C) to be safe. The battery still powers things; it just won't take a charge. Keep it indoors or insulated, or use a self-heating battery. More: lithium batteries in cold weather.

4. Is a fuse, breaker or connection open?

Check every fuse and breaker between the panels, the controller and the battery, then the connections themselves: loose battery cables, badly crimped lugs and loose MC4 connectors stop charging, and loose connectors can overheat and melt. Cables that are too thin lose enough voltage to cause the same trouble.

5. Are the controller's settings right?

A controller set for lead-acid, or with its charge voltage or current set too low, can stop short of charging a lithium battery properly. Pick the profile that matches your battery. If your controller takes orders from a battery's BMS, it will also stop when the BMS says the battery is full or too cold, which is normal.

6. Is anything wired backwards?

Panel or battery wires swapped (positive to negative) stop the controller from charging. Panels wired with too much voltage for the controller do the same, and can damage it.

7. On a power station: is the input inside its window?

Power stations accept solar only inside a voltage range. An EcoFlow DELTA 2, for example, takes 11-60 volts, up to 15 amps and 500 watts. One small panel in weak light can fall under the minimum; too many panels in series can go over the maximum. Most also won't charge outside a temperature range (the DELTA 2: 32-113°F / 0-45°C). Your model's manual lists both.

Still stuck?

Write down the panel voltage, battery voltage and what the controller or power station shows, then compare them with the steps above. If the numbers look right and it still won't charge, contact the maker's support with those readings.