Deep Cycle Marine Battery

Best BCI Group 51 and Group 51R Batteries

BCI Group 51 and Group 51R batteries are very popular automotive and marine batteries, used as starting/cranking batteries and for powering other devices while the engine is turned off.

While older group 51/51R batteries were almost exclusively wet/flooded starting lead-acid batteries, modern group 51/51R batteries are very often designed as dual-purpose, maintenance-free AGM batteries, with lithium group 51/51R batteries slowly becoming more and more popular.

Published: May 14, 2021.

acdelco acdb24r 1

BCI Group 51 and Group 51R Batteries Features and Specifications

BCI Group 51 and Group 51R batteries feature the same physical dimensions, but they differ in terminal orientation - group 51 batteries feature a positive terminal on the left, while group 51R batteries feature a positive terminal on the right side of the battery (hence the 51R ).

Physical dimensions of the group 51/51R batteries is very similar to the group 22NF batteries (L x W x H):

- Group 22NF Batteries: 9 7/16 x 5 1/2 x 8 15/16 inches (9.4375 x 5.5 x 8.9375 inches, 240 x 140 x 227 mm),

- Group 51/51R Batteries: 9 3/8 x 5 1/16 x 8 13/16 (9.375 x 5.0625 x 8.8125 inches, 238 x 129 x 223 mm).

The physical difference between group 22NF and group 51/51R is rather small and group 22NF batteries very often can easily fit into the battery compartments intended for group 51/51R batteries, but sometimes they can't.

Another problem is that some manufacturers offer batteries in group 22NF dimensions, but they advertise them as group 51/51R batteries - such batteries due to the larger volume also feature larger capacity, stronger cranking currents, longer RC values, etc.

The following comparison chart lists some of the most popular group 51/51R batteries with their most important features and specifications:

Model Battery Type Cell Type Ah CCA MCA RC Weight (lbs/kg) Review
ACDelco ACDB24R Dual Purpose AGM 45 325 390 70 29.11 lbs; 13.2 kg -
Antigravity 51R-30-RS Starting LiFePO4 30 - 1200 - 11.7 lbs; 5.3 kg -
Deka/East Penn 8AMU1R Starting AGM - 320 400 45 25 lbs; 11.3 kg -
Delphi BU9051P MaxStart Dual Purpose AGM 46 325 390 60 29.5 lbs; 13.4 kg -
Optima 8071-167 D51 Dual Purpose AGM 38 450 575 66 26 lbs; 11.8 kg Optima D51 and D51R
Optima 8073-167 D51R Dual Purpose AGM 38 450 575 66 26 lbs; 11.8 kg
XS Power D5100 XS Dual Purpose AGM 60 - 745 100 39.6 lbs; 18.0 kg -
XS Power D5100R XS Dual Purpose AGM 60 - 745 100 39.6 lbs; 18.0 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.

As one can see, XS Power D5100 and XS Power 5100R feature the highest 20h capacity, strongest CA/CCA ratings among the AGM batteries, and the longest RC values. Also, they are the heaviest batteries on the chart.

Reason? Their physical dimensions are closer to group 22NF than to the dimensions of group 51/51R.

Note: Official XS Power site lists somewhat different information regarding the capacity, CA, RC, weight, etc. So, before ordering any battery, not just XS Power, check twice what kind of battery You are actually ordering ...

xs d5100r battery

 On average, a good group 51/51R AGM battery features a nominal capacity of 38-45 Ah, 320-450 Amps CCA rating, 390-575 Amps CA rating, 60-70 min RC values and they weigh 25-30 pounds.

Thanks to the AGM technology, most group 51/51R batteries are labeled as "dual-purpose" batteries, and are suitable not only for automotive/marine use, but also for light industrial applications.

Lithium group 51/51R batteries are not as common as some other battery groups.

antigravity 51r lithium

Antigravity Group-51R car battery is an ultralight starting battery offered in two versions:

- 51R-24-RS: racing only battery, featuring a nominal capacity of 24Ah, but featuring CA value of 1000 Amps at only 8.5 pounds (~3.85 kg).

- 51R-30-RS: drop-in battery replacement, featuring a nominal capacity of 30 Ah, and featuring a CA value of 1200 Amps at only 11.7 pounds (~5.3 kg).

Personally, for racing cars weight savings of 18-20 pounds more than justifies the price difference between lead-acid AGM and lithium batteries, but for passenger cars, I am not that sure.

But, it is good to know in what direction the things are developing :)


optima d51r battery

Long Story Short: If You are looking for a new group 51 and group 51R battery, consider tried and tested sealed, maintenance-free AGM battery from reputable brands.

Model Battery Type Cell Type Ah CCA MCA RC Weight (lbs/kg) Review
ACDelco ACDB24R Dual Purpose AGM 45 325 390 70 29.11 lbs; 13.2 kg -
Antigravity 51R-30-RS Starting LiFePO4 30 - 1200 - 11.7 lbs; 5.3 kg -
Deka/East Penn 8AMU1R Starting AGM - 320 400 45 25 lbs; 11.3 kg -
Delphi BU9051P MaxStart Dual Purpose AGM 46 325 390 60 29.5 lbs; 13.4 kg -
Optima 8071-167 D51 Dual Purpose AGM 38 450 575 66 26 lbs; 11.8 kg Optima D51 and D51R
Optima 8073-167 D51R Dual Purpose AGM 38 450 575 66 26 lbs; 11.8 kg
XS Power D5100 XS Dual Purpose AGM 60 - 745 100 39.6 lbs; 18.0 kg -
XS Power D5100R XS Dual Purpose AGM 60 - 745 100 39.6 lbs; 18.0 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.

Just be sure that it fits your battery compartment and that its performances are good enough for your needs and requirements.



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