Battery Equivalents and Replacements

Group 75 Batteries - Dimensions, Features, and Recommendations

BCI Group 75 batteries are automotive and light industry batteries, designed mostly as starting or dual-purpose batteries with very good starting features.

As such, BCI Group 75 batteries are commonly used in cars, light trucks, and other vehicles, where they are used for starting internal combustion engines but also for powering various other loads like pumps, winches, lights, etc.

Updated: August 28, 2023.

odyssey 75 pc1230

Group 75 Battery Specifications and Features

Modern BCI Group 75 Batteries are mostly AGM (Absorbent Glass Mat) SLA (Sealed Lead Acid) batteries, designed with increased vibration resistance in mind and thanks to the modern technologies, with very vague difference between starting/cranking and dual-purpose batteries - most 'starting' batteries are made with Start/Stop applications in mind, combined with powering various other devices while the main engine is off.

Similarly, dual-purpose batteries are designed for powering all kinds of loads while the main engine is turned off, but they are also designed to provide large amounts of current required to crank the gas/diesel engines.

The most popular group 75 batteries are given in the following comparison chart:

Model Battery Type
Cell Type
Capacity (Ah)
RC (min)
Weight (lbs/kg)
Delphi BU9075DT MaxStart Starting
41.0 lbs; 18.6 kg
Odyssey 75-PC1230 Dual Purpose
45.5 lbs; 20.6 kg
Odyssey 75/86-PC1230DT Dual Purpose
45.5 lbs; 20.6 kg
Odyssey ODP-AGM7586 Dual Purpose
43.4 lbs; 19.7 kg
Optima 8022-091 75/25 RedTop Starting
33.1 lbs; 15.0 kg
Optima 8042-218 D75/25 YellowTop Dual Purpose
37.8 lbs; 17.2 kg

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As one can see, group 75 batteries feature a nominal (20h) capacity in the 44-60 Ah range, they feature CCA in the 620-760 Amps range, 770-910 Amps MCA, and RC value of ~90-110 minutes.

Also, they weigh between 33.1 and 45.5 pounds (15.0 - 20.6 kg).

optima 75 25 red top

By default, group 75 batteries feature side battery terminals (positive to the left), but some models feature both top and side terminals, often being additionally labeled with 'DT' (Dual Terminals) letters.

Some dual terminal group 75 batteries are labeled as 'group 75', some are labeled as 'group 75/25', and some models as 'group 75/86' batteries - this is due to the similar dimensions between BCI battery groups 25, 75, and 86:

  • BCI Group 25 Battery: 9 1/16 x 6 7/8 x 8 7/8 inches (230 x 175 x 225 mm),
  • BCI Group 75 Battery: 9 1/16 x 7 1/16 x 7 5/16 inches (230 x 179 x 186 mm),
  • BCI Group 86 Battery: 9 1/16 x 6 13/16 x 8 inches (230 x 173 x 203 mm).

As one can see, physical dimensions differ, but not by much. Because of that, some manufacturers offer '75' and/or '75/25' and/or '75/86' size batteries.

delphi bu9075dt

Of course, when ordering a new group 75 battery, it is very important to check the size of the battery compartment and the actual size of the new battery.

Lithium Group 75 Batteries

Lithium group 75 batteries are not yet available on the market, at least not in larger numbers.

These batteries are mostly based on Lithium Iron Phosphate (LiFePO4) chemistry and feature similar capacity as AGM group 75 batteries, but they support a much larger number of charging/discharging cycles.

A maximum current of lithium group 75 batteries is limited for safety reasons via built-in Battery Management Systems (BMS) to ~1C, with surge current in the 1.5-2.0C range for 3-5 seconds, model-dependent.

Starting group 75 lithium batteries are very rare, if available at all.

Note: when we discuss group 75 batteries, we are referring to lead-acid group 75 batteries, unless otherwise stated.

How to Charge Group 75 Battery?

If the battery is installed in the car or any other vehicle that features an onboard battery charging system, let it charge the battery.

It is a good practice to check the voltage on the battery and terminal connections periodically - AGM batteries are practically maintenance-free batteries, but they must be properly connected to the car/truck in order to work as intended.

Those batteries that are not charged by an alternator connected to the internal combustion engine should be charged using smart AGM battery chargers that analyze the battery prior to charging and adjust the charging process according to the battery's condition.

Since their capacity varies between 44-48 Ah (spiral-wound batteries) and 55-60 Ah (flat plates), they can be charged with battery chargers featuring an output current of 5 - 10 Amps.

Such a battery charger can recharge 50Ah battery discharged down to 50% DoD in around 3 hours, depending on the battery condition, temperature, and similar.

Note: some group 75 batteries, when charged using battery chargers, prefer currents in the 5-6 Amps range to avoid overstressing the battery - if unsure, check the battery documentation.

Group 75 Battery as Inverter Battery?

When being used in the car group 75 batteries are often used for powering various devices via car power inverters.

When the cigarette lighter adapter is used, the current is limited to mostly 10 Amps, leading to the maximum inverter output power of ~100-120 watts.

However, if the inverter is connected directly to the battery, stronger 300-500W power inverters may be used.

On average, 300W power inverters feature an efficiency of ~85%, requiring ~350 watts from the battery (30 Amps @12V).

Since RC values for group 75 batteries vary between 100 and 110 minutes, group 75 batteries may provide ~250 watts (output power) for up to 50-55 minutes without being drained below 50% DoD.

But, for something like that, one needs a good 300W pure sine wave power inverter.

Similarly, group 75 dual-purpose batteries may be used as trolling motor batteries, large fish finder batteries, solar batteries, in various light-industrial applications, etc.

Just be sure to recharge the battery as soon as possible and not to discharge it below 80%, preferably below 50%.

Note: if the battery is regularly discharged below 50%, its ability to crank internal combustion engines will be diminished.

optima d75 25 yellow top

Long Story Short: Group 75 batteries are able to easily crank gas and diesel engines and still be able to power other devices when the main engine is offline.

They are AGM maintenance-free batteries that often feature dual terminals and are built to fit either group 75, group 75/25, or group 75/86 battery compartments.

As always with the batteries, be sure to check the terminal orientation and actual size of both the new battery and the battery compartment.

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