Battery & storage
Enter your battery size and grid charger rate. Get an estimated time to go from empty to full.
How it works
Step 1
This is the maximum kW your inverter can push into the battery from the grid, usually published in the spec sheet, or check the battery inverter pairing tool.
Step 2
Charging from partially full takes proportionally less time than from fully empty.
Step 3
If you're planning overnight off-peak charging, confirm this time fits within that window, and see the time of use arbitrage tool for the savings case.
Charge time depends on the battery's usable capacity divided by the charging rate, with a small efficiency loss applied since some energy is lost converting AC grid power to DC for battery storage. The limiting factor for charging speed is whichever is lowest among the inverter's maximum charging rate, the electrical panel's available capacity, and the battery's own maximum accepted charge rate, a constraint explained in the Department of Energy's inverter basics guide, so a fast charger paired with a slower-rated battery won't charge any faster than the battery itself allows. The hybrid inverter sizing calculator in our Inverters & Equipment category covers choosing an inverter that won't become this bottleneck.
Grid charging delivers a steady, consistent power rate for the entire charging session, limited only by equipment ratings, while solar charging power naturally fluctuates throughout the day based on sun angle, cloud cover, and time of day, a pattern documented in NREL's solar resource data. This makes grid charge time much easier to predict precisely, and often faster in absolute terms since it isn't limited by available sunlight. The charge time from solar calculator covers that more variable scenario.
Grid charging isn't only a fallback for homes without solar. Many systems use it strategically, such as topping off the battery overnight during cheap off-peak electricity rates as part of a time of use arbitrage strategy, or as a precaution to make sure the battery is completely full before an anticipated storm regardless of the previous day's solar production. The time of use arbitrage tool covers that specific strategic use case, and the quick financing comparison tool in our Financing category helps weigh whether the electricity savings from this strategy offset the system's cost over time.
If you're planning charging around a specific time window, like overnight off-peak hours, compare this result against that window to confirm the battery will be full in time, and check the battery inverter pairing tool if you're unsure about your equipment's actual charging rate limits. If you're financing the battery itself, the financing for battery addition calculator in our Financing category covers the cost side of this decision. The hybrid inverter sizing calculator checks whether your inverter can handle this result.
Questions
A 13.5 kWh battery at 90% depth of discharge charging from a 5 kW charger takes about 2.6 hours to fully recharge from empty, accounting for a small charging efficiency loss.
Grid charging typically delivers a steady, consistent power rate limited only by the charger and inverter, while solar charging power fluctuates throughout the day based on sun angle and weather. This makes grid charge time easier to predict and often faster in absolute terms.
Not necessarily. Many systems use grid charging strategically, such as topping up overnight during cheap off-peak rates for time of use arbitrage, or as a backup method to make sure the battery is full before an anticipated storm, even when solar remains the primary daily charging source.
The inverter's maximum charging rate, the electrical panel's available capacity, and the battery's own maximum charge rate rating all can act as the limiting factor, whichever is lowest determines your actual maximum charging speed regardless of how much grid power is theoretically available.
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