Group 78 Batteries - Dimensions, Features, and Recommendations

BCI Group 78 batteries is a group of car and light trucks batteries but also used in marine and light industrial applications as starting and as general, dual-purpose batteries.

BCI Group 78 batteries are often used in 'Stop-and-Go' automotive applications, requiring the batteries to provide large currents very often and to be recharged quickly - such applications require tough and durable, high-quality batteries.

northstar nsb agm78

Group 78 Batteries - Dimensions and Specifications

BCI Group 78 batteries are medium size lead-acid batteries, with practically all modern batteries being made as Sealed Lead-Acid (SLA) Absorbent Glass Mat (AGM) batteries.

Gel-cell, wet/flooded, and lithium iron phosphate (LiFePO4) group 78 batteries are not as common.

Physical dimensions of the group 78 batteries is very similar to several other battery groups, allowing these batteries to be used almost interchangeably. Here is the list of several of such groups with their maximum dimensions (L x W x H):

- Group 78: 10.25 x 7.0625 x 7.6875 inches (26 x 17.9 x 19.6 cm),

- Group 34: 10.25 x 6.8125 x 7.875 inches (26 x 17.3 x 20 cm),

- Group 24: 10.25 x 6.8125 x 8.875 inches (26 x 17.3 x 22.5).

As one can see, group 78 is somewhat wider than the groups 34 and 24, but also somewhat lower.

Another very important difference is that group 78 batteries feature front 3/8" terminal posts (positive to the left, negative to the right).

Since groups 34 and 78 are so similar in dimensions, many manufacturers offer batteries labeled as '34/78' - these batteries feature both top SAE terminals (like group 34 batteries have) and side 3/8" terminals (like group 78 batteries have). Also, such batteries often have letters 'DT' (Dual Terminals) as part of their labels in order to distinguish them from 'common' group 34 and group 78 batteries.

odyssey 34 78 pc1500

Note: just in case, whenever changing the battery (not just group 34, 34/78 or 78), always check the size of the battery compartment and the actual battery size that You intend to buy - battery compartments generally have some spare room to accommodate the batteries that are somewhat larger, but better safe than sorry.

The following comparison chart lists some of the best and most popular group 78 and group 34/78 batteries with some of their features and specifications:

Model Battery Type Chemistry Ah CCA MCA RC Weight (lbs/kg) Review
ACDelco 78AGM Starting AGM 60 740 890 115 37.8 lbs; 17.2 kg -
Delphi BU9078 MaxStart Starting AGM 55 775 - 120 43 lbs; 19.5 kg -
Northstar NSB-AGM34/78 Dual Purpose AGM 65 880 1050 134 51 lbs; 23.1 kg -
Northstar NSB-AGM78 Dual Purpose AGM 65 880 1050 134 51 lbs; 23.1 kg -
Odyssey 34/78-PC1500DT Dual Purpose AGM 68 850 1050 135 49.5 lbs; 22.4 kg Odyssey 34/78
Odyssey 78 PC1500 Dual Purpose AGM 68 850 1050 135 49.5 lbs; 22.4 kg -
Optima 8004-003 34/78 RedTop Starting AGM 50 800 1000 100 38.8 lbs; 17.6 kg Optima 34/78 RedTop
Optima 8014-045 D34/78 YellowTop Dual Purpose AGM 55 750 870 120 43.5 lbs; 19.7 kg Optima D34/78 YellowTop
Optima 8078-109 78 RedTop Starting AGM 50 800 1000 100 39.5 lbs; 17.9 kg -

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.

optima 34 78 yellowtop

On average, group 34/78 and group 78 batteries feature nominal (20h) capacity in the 50-70 Ah range, a nominal voltage of 12 volts, 700-900 CCA, 850 - 1050 MCA, and 100-135 minutes RC. Also, they weigh between 38 and 51 pounds (~17 - 23 kg).

Starting group 34/78 and group 78 AGM batteries are optimized for providing a short but strong burst of energy and are generally lighter than dual-purpose batteries. Starting batteries should be used only as cranking batteries and for powering light loads while the engine is turned off - alarm/security systems and similar.

Dual-purpose group 34/78 and group 78 AGM batteries feature thicker plates and are thus heavier. But, they are also able to provide strong currents for short periods of time and they also tolerate deep discharge cycle applications, much better than starting batteries.

People having cars and trucks with devices that must operate when the main engine is turned off should go for dual-purpose batteries. Such devices include loads like various pumps, winches, compressors, multimedia devices, chargers, inverters, etc.

However, note that even the dual-purpose batteries last longer when they are not discharged too deep - when discharged down to 50% DoD some models tolerate 700-900 charging/discharging cycles easily - Odyssey and NorthStar models, for example.

The prices of group 34/78 and group 78 batteries vary depending on their capacity, warranty, discharge characteristics, and other important features:

NorthStar and Odyssey are premium batteries that often cost more than other batteries, but, what you pay is what you get - a tough, durable, and reliable battery that can withstand a lot of use and even some abuse (just don't do it, unless really unavoidable).

Optima batteries with their spiral-wound cells are relatively light and vibration resistant, they offer excellent performances considering their price.

Other battery brands (ACDelco, Delphi, etc.) manufacture good batteries that come at acceptable prices and when found on sale, can be a great money-saver.

optima 34 78 redtop

How to Charge Group 34/78 and Group 78 Batteries?

When the battery is connected to the car's electric system, it is being charged and monitored by the very same car's electric system - when the car's engine is ON, the alternator produces electricity and the part of the electricity is used for recharging the battery.

If there is an issue with the alternator and/or battery, the car's electric system will notify the user - most modern cars will display an error message of some kind (code or detailed text, car-dependent).

However, batteries that are used in industrial applications should be charged using smart AGM battery chargers that can analyze the battery and adjust the charging process to the battery's condition - desulphation and cell-equalization modes are very important for prolonging the operating time of such batteries.

For batteries in 60-70 Ah capacity range, advanced 10-15 Amps AGM battery chargers are recommended:


Long Story Short: Group 78 and 34/78 batteries are common car/truck and light industry batteries, often available at local hardware shops and online stores. Their performances do come at a certain price, but a good battery is almost never appreciated until badly needed.

Model Battery Type Chemistry Ah CCA MCA RC Weight (lbs/kg) Review
ACDelco 78AGM Starting AGM 60 740 890 115 37.8 lbs; 17.2 kg -
Delphi BU9078 MaxStart Starting AGM 55 775 - 120 43 lbs; 19.5 kg -
Northstar NSB-AGM34/78 Dual Purpose AGM 65 880 1050 134 51 lbs; 23.1 kg -
Northstar NSB-AGM78 Dual Purpose AGM 65 880 1050 134 51 lbs; 23.1 kg -
Odyssey 34/78-PC1500DT Dual Purpose AGM 68 850 1050 135 49.5 lbs; 22.4 kg Odyssey 34/78
Odyssey 78 PC1500 Dual Purpose AGM 68 850 1050 135 49.5 lbs; 22.4 kg -
Optima 8004-003 34/78 RedTop Starting AGM 50 800 1000 100 38.8 lbs; 17.6 kg Optima 34/78 RedTop
Optima 8014-045 D34/78 YellowTop Dual Purpose AGM 55 750 870 120 43.5 lbs; 19.7 kg Optima D34/78 YellowTop
Optima 8078-109 78 RedTop Starting AGM 50 800 1000 100 39.5 lbs; 17.9 kg -

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.

When choosing the right model, be sure to choose according to your own needs and requirements.