What is a Group 121R Battery: Technical Information and Comparison with Alternatives

Group 121R Battery Dimensions

Battery of this group has the positive post terminal located on the right. It is marked with the letter "R" because this post terminal position is called Reverse Polarity of Battery. Most batteries have it on the left side. If you want the positive post terminal to be on the left, you can turn around the 121R battery and use it as a group 121 battery, because they have identical dimensions. This will allow you to use the positive post on the left. Make sure you have enough cable length to reach the terminals, because in the turned position the terminals can be located a little further.

Battery Design

Dimensions and Sizes (Length x Width x Height)
8.25'' x 7'' x 8.5'' Inches 208 x 177 x 215 Millimeters

Group 121R Battery Post Terminals

Post Terminal Types and Locations	Posts Used
	Type "A" or manufacturer's custom post design

Group 121R Battery Voltage and Current Characteristics

Volts	Cells	CCA Range
12	6	410-600

Best Group 121R Batteries

List of recommended batteries

Good Choice	SLI121R Duracell Ultra Flooded 550CCA BCI Group 121R Car and Truck Battery Cold Cranking Amps (CCA): 550, Battery Group: 121R Type: Lead-Acid Warranty: 24 months Check Price	Check Price
Good Choice	EverStart Maxx Lead Acid Automotive Battery, Group Size 121R Cold Cranking Amps (CCA): 600, Battery Group: 121R Type: Lead-Acid Warranty: 36 months Check Price	Check Price

Group 121R Alternatives and Closest Battery Groups by Dimensions

There are no direct interchangeable alternatives for group 121R battery if we speak about dimensions, but if your battery space hasn't strict limits, you can choose a little bigger or smaller battery group. If your battery compartment cannot accommodate a larger battery, you can choose a smaller one. In both cases, you must securely fasten your new battery with a battery holder. If your battery holder can't hold the alternative battery group, you can buy a universal battery holder to fit in different types of batteries.

Closest but not Identical Size Battery Groups

Battery groups in this section below are not identical to the group 121R battery, they can be a little bigger or smaller. Please pay attention to the post terminal types and their location

Closest Groups that Have Slightly Smaller Dimensions

Smaller batteries can have less capacity, performance, and power in comparison with 121R group.

Battery Group Number	Dimensions	Shape	Volts	Cells	Post Terminal Type
Group 121R Battery	8.25'' x 7'' x 8.5'' in. 208 x 177 x 215 mm Positive post on the Right		12	6	"A"
Group 21R Battery	8.1875'' x 6.8125'' x 8.75'' in. 208 x 173 x 222 mm Positive post on the Right		12	6	"A", "A2"
Group 21 Battery	8.1875'' x 6.8125'' x 8.75'' in. 208 x 173 x 222 mm		12	6	"A", "A2"
Group 26R Battery	8.1875'' x 6.8125'' x 7.75'' in. 208 x 173 x 197 mm Positive post on the Right		12	6	"A"
Group 26 Battery	8.1875'' x 6.8125'' x 7.75'' in. 208 x 173 x 197 mm		12	6	"A", "A2"
Group 140R Battery	8.125'' x 6.9375'' x 7.5'' in. 207 x 175 x 190 mm Positive post on the Right		12	6	"A"
Group 99R Battery	8.125'' x 6.9375'' x 6.9375'' in. 207 x 175 x 175 mm Positive post on the Right		12	6	"A1"
Group 99 Battery	8.125'' x 6.9375'' x 6.9375'' in. 207 x 175 x 175 mm		12	6	"A1"
Group 61 Battery	7.5625'' x 6.375'' x 8.875'' in. 192 x 162 x 225 mm		12	6	"A"

Closest Large Dimensions

Bigger batteries can have more capacity and power compared to 121R batteries.

Battery Group Number	Dimensions	Shape	Volts	Cells	Post Terminal Type
Group 121R Battery	8.25'' x 7'' x 8.5'' in. 208 x 177 x 215 mm Positive post on the Right		12	6	"A"
Group 75 Battery	9.0625'' x 7.0625'' x 7.3125'' in. 230 x 180 x 186 mm		12	6	"S"
Group 72 Battery	9.0625'' x 7.0625'' x 8.25'' in. 230 x 179 x 210 mm		12	6	"S"
Group 73 Battery	9.0625'' x 7.0625'' x 8.5'' in. 230 x 179 x 216 mm		12	6	"S"

How to Get 24 Volts from 12V of a 121R Battery Group

If you need 24 Volts, you can connect two group 121R batteries in series to double the voltage. The voltage of a series connection is equal to the sum of the voltages of all its batteries. If one 12V lead-acid battery is connected to another 12V lead-acid battery, you have 24V total power output. Each battery must be fully charged and completely isolated from the other before connecting them in series, or there will be damage to at least one of them.

Increasing a Capacity of 121R Batteries with a Parallel Connection

If you need to increase current capacity and reduce charging time, connect batteries in parallel. When group 121R batteries are in parallel, their voltage is equal to the voltage of one battery, while current capacity equals to the sum of all its battery capacities. If you have two 12V lead-acid batteries with 60 Ah capacity and you connect them in parallel, you'll get 12 Volts with 120 Ah.