Best Lead-Acid and Lithium 1 kWh Solar, Marine, Automotive, and Light Industrial Batteries

Lead-acid and lithium 12V batteries with a nominal capacity of 85-100+ Ah are able to store plenty of energy and deliver at least 1000 kWh of energy when discharged under certain conditions.

Unlike lithium batteries, lead-acid deep cycle batteries are very susceptible to high discharge currents in terms of capacity and energy loss. Hence, most of the modern solar and similar systems that require deep-discharge batteries that cycle a lot are based on lithium batteries.

Published: April 11, 2022.

Discharge Issues With Lead-Acid and Lithium Batteries

For a battery to qualify as a "1 kWh battery", it must be able to deliver 1000 Wh (1 kWh) of energy on a single battery charge.

In theory, the ideal 12V battery must feature a nominal capacity of 83.3Ah to feature an energy capacity of 1000 Wh.

However, both lead-acid and lithium batteries have a nominal voltage of 12V, while the actual voltage varies with the battery discharge level and the discharge current. Also, as the discharge current is increased, the actual capacity is decreased - this may be very problematic for lead-acid batteries, while lithium batteries are not as nearly as susceptible to the discharge current as the lead-acid batteries.

Since lithium batteries feature an actual voltage of 12.8 volts which decreases slightly with the increase of discharge current and with the decrease of the remaining charge level, lithium batteries with a nominal capacity of ~85 Ah are able to deliver 1000 Wh (1 kWh) on a single battery charge.

On the other hand, when wet/flooded, AGM and Gel-Cell lead-acid batteries are being discharged with 1C currents, their actual capacity drops down to 50-72% of the batteries' nominal 20h capacity.

For example, the best 12V 100Ah lead-acid batteries feature 1 kWh capacity when they are discharged within 5 hours (0.2C). Anything faster than that and the lead-acid batteries are not able to deliver 1000Wh of energy.

When looking for a 1 kWh battery, go for either BCI Group 27 batteries or preferably for BCI Group 31 batteries.

BCI Group 27 Batteries

BCI Group 27 batteries feature physical dimensions of 12 1/16 x 6 13/16 x 8 7/8 inches (12.0625 x 6.8125 x 8.875 inches; 306 x 173 x 225 mm) with the most popular models being listed in the following comparison chart:

Note: Amazon affiliate links ("Model" column) open in the new windows, feel free to check them for the most up-to-date offers and prices.

As one can see, some of the lead-acid and lithium group 27 batteries feature required nominal capacity, but one has to check the exact constant power discharge charts of the lead-acid batteries in order to determine under what conditions these batteries may be considered as "1 kWh batteries".

For example:

Universal Power Group UB121000 AGM Deep Cycle Battery is one of the most popular AGM deep-cycle group 27 batteries, commonly used in various applications that require a well-balanced and reliable, but also an affordable battery.

The following chart shows UPG UB121000 constant power discharge characteristics at 77°F (25°C), with the values given in Watts (W):

Note: The value for 5 hr constant discharge power down to 10.20 V is given as an approximation because the official data given by UPG is - wrong. At least last time we checked ...

As one can see, the energy capacity of the UPB UB121000 depends on the discharge power:

- 1h: 620.4 Wh,

- 2h: 735.4 Wh,

- 3h: 826.5 Wh,

- 4h: 858.8 Wh,

- 5h: 890 Wh,

- 8h: 996 Wh,

- 10h: 1112 Wh,

- 20h: 1200 Wh.

So, despite having a nominal capacity of 12V and a nominal (20h) capacity of 100 Ah, the UPG UB12000 battery can be considered as a 1 kWh battery only when being discharged for a period of ~8-10 or more hours.

Another problem with lead-acid batteries is that not all manufacturers provide exact constant current and constant power discharge charts.

BCI Group 31 Batteries

BCI Group 31 batteries feature physical dimensions of 13 x 6 13/16 x 9 7/16 inches (~13 x 6.8 x 9.44 inches, 330 x 173 x 240 mm) with the most popular models being listed in the following comparison chart:

Note: Amazon affiliate links ("Model" column) open in the new windows, feel free to check them for the most up-to-date offers and prices.

As one can see, almost all lead-acid and lithium group 31 batteries feature required nominal capacity - again, one has to check the exact constant power discharge charts of the lead-acid batteries in order to determine under what conditions these batteries may be considered as "1 kWh batteries".

Also, some of the group 31 lithium batteries feature nominal capacity in the 120-150+ Ah range and are able to store and what is more important, deliver much more than the required 1 kWh of energy.

For example:

Odyssey 31M-PC2150 (ODX-AGM31) AGM Marine Dual Purpose Battery is one of the best group 31 batteries in terms of its discharge performances.

It is an excellent lead-acid AGM battery that comes in several versions that differ practically only in the battery terminals, with their charging/discharging characteristics being the same.

The following chart lists constant power and constant current discharge values of the Odyssey 31-PC2150 (ODX-AGM31) batteries:

Unlike the UPG UB121000 battery which is able to deliver ~996 Wh during the period of at least 8 hours, the Odyssey 31-PC2150 battery is able to provide 996.8 Wh (very close to 1 kWh) during the period of 4 or more hours.

This is not a surprise, since Odyssey 31M-PC2150 (ODX-AGM31) battery is a premium AGM battery that is used for mission-critical and other similar applications where a tough and durable battery is required.

Few Final Words

If You are looking for a 1 kWh battery, depending on other requirements like number of supported charging/discharging cycles, discharging current, charging current, power surges and similar, go for either lithium 12V 85-100+ Ah battery or for lead-acid 12V 100+ Ah battery.

Note: some brands offer group 31 24V, 36V, and 48V lithium batteries - these batteries are also 1+ kWh batteries although their nominal capacities are lower since their voltages are higher ...