Group 4D, 6D, and 8D Batteries - Dimensions, Features, and Recommendations

BCI Group 4D, 6D, and 8D batteries are large and heavy commercial batteries, often used for off-the-grid applications, as solar batteries, as RV house batteries, for security, medical and standby applications, for powering various industrial vehicles and applications, etc.

BCI Group 4D, 6D, and 8D lead-acid batteries were commonly Absorbent Glass Mat (AGM) or Gel-Cell Sealed Lead Acid (SLA) batteries, but are now being phased out in favor of Lithium Iron Phosphate (LiFePO₄) 4D, 6D, and 8D batteries.

But, AGM and Gel-Cell lead-acid batteries are still going on strong in applications where lightweight design and high cycling abilities are not of greatest importance.

Updated: February 23, 2022.

On This Page:

• Group 4D, 6D, and 8D Batteries Features and Specifications
• Lead-Acid vs. Lithium 4D, 6D, and 8D Batteries
• 4D, 6D, and 8D Batteries as Off-the-Grid Batteries
• 4D, 6D, and 8D Batteries as Sump Pump Backup Batteries
• The Best 4D, 6D, and 8D Deep Cycle Battery - Pick the Right One 

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Group 4D, 6D, and 8D Batteries Features and Specifications

Group 4D, 6D, and 8D batteries are large batteries with their maximum dimensions (L x W x H) of:

- 4D batteries: 20 3/4 x 8 3/4 x 9 7/8 inches (527 x 222 x 250 mm),

- 6D batteries: 20 3/4 x 10 x 10 1/4 inches (527 x 254 x 260),

- 8D batteries: 20 3/4 x 11 1/8 x 9 7/8 inches (527 x 283 x 250 mm).

We emphasize these 'maximum dimensions' since some of the BCI group 8D batteries are closer to group 6D or group 4D, but they are still labeled as 8D battery group and similar.

Whenever changing the battery (or batteries) always check the battery chemistry, capacity, discharge features, but also its actual dimensions.

Because of their different dimensions and chemistries,  4D, 6D, and 8D batteries vary in weight (~45 - 190 pounds), 20h capacity (200-400 Ah), Reserve Capacity (RC; 400-960 minutes), CCA values (~1350 - 2250 Amps, if allowed), MCA values (~1700 - 2700 Amps, if allowed), number of charging/discharging cycles, etc. But they also differ in the price, too.

Note: some deep cycle 4D, 6D, and 8D batteries, although large and powerful, are intended only for (relatively) low current discharge applications and don't even mention their CA/MCA values - don't use them as cranking batteries, except for relatively small engines. Most lithium batteries based on the Lithium Iron Phosphate chemistry feature very low weight, high capacity, but the discharge current is usually limited to 1C, with 2-3C currents being allowed for only a few seconds (even that may be an issue).

The following chart lists the most popular group 4D, 6D, and 8D batteries with their most important features and specifications:

As one can see, group 4D, 6D, and 8D batteries are large and strong batteries that can store and deliver large amounts of energy easily that can make damage and hurt people and animals.

Most of these batteries come with carrying handles which sounds rather convenient, but IMHO, lead-acid 4D, 6D, and 8D batteries should be carried by at least two adults that are used to physical labor - seriously, people get injured when trying 'just to move it a little bit' or something similar.

Group 4D, 6D, and 8D batteries are commonly labeled as 'Deep Cycle' or as 'Dual Purpose' while starting group 4D, 6D, and 8D batteries being very rare, if present at all, due to the advances in Gel-Cell/AGM batteries.

Some manufacturers label their models as 'deep cycle' and state their CCA/MCA values, which are in some cases even better than CCA/MCA values of some 'dual purpose' models.

But, like with everything in life, performances come at a certain price.

Prices may differ significantly, but so do the warranties, number of supported cycles, relative capacities, CCA/MCA, and other values.

Lead-Acid vs. Lithium 4D, 6D, and 8D Batteries

Most 4D, 6D and 8D lead-acid batteries are AGM SLA batteries, with few Gel-Cell SLA models.

Lithium Iron Phosphate 4D, 6D, 8D batteries are becoming more and more popular, especially for applications where batteries must support a large number of charging/discharging cycles, where batteries' weight is of great importance, and similar.

The most important differences between lead-acid and LiFeP0₄ batteries are:

- Depth of Discharge: when lead-acid batteries are pushed down to 80-100% DoD, the number of their supported charging/discharging cycles is reduced down to 200-400 cycles. And when they are discharged, it is highly recommended to recharge them quickly in order to prevent capacity loss.

On the other hand, when the LiFePO4 batteries are discharged down to 80-100% DoD, they support 2000-4000+ charging/discharging cycles, and that is a huge difference.

In order to increase the number of charging/discharging cycles of the lead-acid batteries, their DoD should be kept around 50% - this increases the number of charging/discharging cycles, but also decreases the actual capacity of the battery (or battery pack).

- High Discharge Current Capacity Loss: capacity of the batteries is usually given for 20h discharge. However, when lead-acid batteries are being discharged with stronger currents, for example, 1C or similar, their actual capacity drops down to 50-70% of their nominal capacity.

Lithium batteries also experience capacity loss when the discharge currents are increased, but just a few percent, at most.

This leads to the much better energy efficiency of lithium batteries.

- Weight of the batteries: lead-acid batteries are usually 2-3x heavier than lithium batteries of the same 20h capacity. But, as said before, as the discharge current is increased, the lead-acid batteries suffer capacity loss. Also, in order to prolong their lifespan, it is recommended to discharge them down to 50% DoD (or perhaps down to 70-80% DoD). Since lithium batteries don't have such issues, lithium batteries are actually 3-5x lighter than lead-acid batteries - and that is a big difference!

- Safety Features/Issues: lead-acid batteries are safe by design - don't abuse them (too much), maintain them properly, and they will serve You for years to come (unless they cycle a lot - in that case, a few months is all that lead-acid batteries can withstand).

On the other hand, lithium batteries can overheat easily, they can burst into flames and even explode if not used properly.

In order to avoid such issues, lithium batteries feature built-in Battery Management Systems (BMS) that protect them from overcharge, over-discharge, high and low temperatures, short circuits, and similar.

- Maximum Discharge Current: a maximum discharge current of the lead-acid batteries depends on the internal resistance of the battery and can be huge. However, normal discharge currents are much lower.

The maximum discharge currents of the lithium batteries are limited by the BMS and are usually around 1C for maximum continuous discharge current and 2-3C for a few seconds (if allowed).

So, although strong discharge currents decrease the actual capacity of the lead-acid batteries, if there is a glitch or something similar in the electric system, BMS may temporarily or permanently disconnect the lithium battery, while lead-acid batteries will continue to power the electric system.

- Chargers: lithium batteries should be recharged using chargers or charge controllers intended for lithium batteries or that have charging modes for lithium batteries. When charging lead-acid batteries, it is recommended to charge them using advanced battery chargers that analyze the battery first and adjust the charging according to the battery condition.

- Charging Time: depending on the battery type (wet/flooded, AGM, Gel-cell) lead-acid batteries can be recharged in 5-10 hours, while most lithium batteries can be fully recharged in 1-2h, with 2-5h being recommended.

- Maintenance: lithium batteries are true maintenance-free batteries, unlike lead-acid batteries.

- Position: lithium batteries may operate in any position, while lead-acid batteries must be positioned upside (wet/flooded), although some models (AGM, Gel-Cell) may operate when positioned on their side.

- Series/Parallel Connections: when connecting the batteries in series and/or parallel, it is very important to use the batteries of the same model, from the same manufacturer, preferably from the same batch.

But, while lead-acid batteries may be connected freely in series and/or parallel, lithium batteries may be connected in series and/or parallel only if explicitly allowed by their manufacturer.

In most cases, large lithium batteries allow 4S4P connections - up to 4 batteries in series and/or up to 4 batteries in parallel, allowing some models to create battery packs with the nominal voltage of 51.2V and capacities in excess of 1600Ah! Such battery packs can be expensive, but they can power large RVs or homes for a long time during blackouts, emergencies, or simply while being off-the-grid ...

- Price of the battery or battery pack: initially, lithium batteries cost more than lead-acid batteries, but in the long run they are cheaper, saving a lot of money in applications that cycle a lot and where the batteries are being discharged with relatively strong currents.

Of course, there are other differences between lead-acid and lithium batteries, but these are the most important ones.

4D, 6D, and 8D Batteries as Off-the-Grid Batteries

4D, 6D, and 8D batteries are very often used in off-the-grid applications for powering homes, RVs, and similar objects and vehicles while mains power is not present.

Because of their advantages over lead-acid batteries, lithium deep-cycle batteries are more and more used for powering homes, RVs, and similar during blackouts, in emergencies, or simply while being off-the-grid.

Since the best lithium batteries support up to 4S4P connections, it is rather easy to create large, although initially expensive battery packs.

For example, a battery pack consisting of 16 Ampere Time 12V 300Ah (Amazon link, opens in the new window) batteries features a nominal voltage of 51.2V, the capacity of 1200Ah, and it weighs only 1008 lbs (~457 kg) - we say "only" because a lead-acid battery pack being able to store ~61 kWh of energy would be simply too heavy for any vehicle.

Note: Lossigy 12V 400Ah (Amazon link, opens in the new window) battery supports 4S10P connections and can be used to build even larger battery packs!

Of course, such large battery packs are not used very often, but they just show how AGM/Gel and lithium batteries can be different.

4D, 6D, and 8D Batteries as Sump Pump Backup Batteries

Sump pump backup batteries are usually BCI Group 31 batteries, but some users prefer sump pump backup systems based on the larger batteries.

Sump pump backup batteries should be reliable batteries being able to withstand years of being on standby, waiting for a blackout or emergency.

While both lead-acid and lithium batteries may be used, sump pump backup batteries don't have to be ultralight batteries and they don't have to support an ultra-large number of charging/discharging cycles.

But, sump pump backup batteries must be able to provide electric energy even if there are strong surges - electric motors that power sump pumps can initially draw rather large currents, even larger than claimed by their manufacturer (no wonder if/when these motors weren't tested over longer periods of time).

Thus, if You are looking for a reliable large sump pump backup battery, go for AGM or Gel-Cell 4D, 6D, or 8D battery.

For example, Renogy 12V 200Ah AGM (Amazon link, opens in the new window) battery weighs 129 pounds (~58.5 kg), supports up to 600 charging/discharging cycles down to 50% DoD, features a standby life of ~10 years (77°F, 25°C), relatively low self-discharge rate (<3% per month, @77°F/25°C), can provide up to 2000 Amps for 5 seconds, and supports maximum charging current of 60 Amps.

Obviously, it is much heavier than similar lithium batteries, but it can provide plenty of current when required, accepts charge very well (for an AGM battery), has a very long standby life, etc.

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The Best 4D, 6D, and 8D Deep Cycle Battery - Pick the Right One

Considering all that has been said, it is hard to pick the "best" one for one very simple reason - people have different needs and requirements and as such, they need different batteries.

For more about these batteries, feel free to check our articles:

- What Is The Best 12 Volt Lithium Battery?

- Best 12V and 24V Lithium Trolling Motor Batteries

- 100Ah Lithium Battery - 12V, 24V, 36V, and 48V Batteries

- Best 12V, 24V, 36V, and 48V Lithium Deep Cycle Battery For a Power Inverter

- 48V Lithium Golf Cart Batteries

- 200Ah Lithium Battery - 12V, 24V, 36V and 48V Models

- Best 12V 300Ah and 400Ah Lithium Deep Cycle Batteries

or feel free to check our Articles and Guides.

If You are looking for large lead-acid batteries, consider models from Renogy, Mighty Max, VMAXTANKS, and similar brands.

And if You are looking for large lithium batteries, consider models from Ampere Time, Chins, Lossigy, Jita, Zooms, and similar brands.

Note: some brands don't even know how to properly spell their names in English, but they do manufacture good batteries ;)

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Long Story Short: Many battery brands manufacture AGM, Gel-Cell, and Lithium group 4D, 6D, 8D batteries, which are used in various applications, including marine, automotive, RV, backup, medical and security systems, etc.

Nonetheless, there are few models whose features stand out, so be sure to choose according to your own needs and preferences.