What Are Group 31 Battery Specs?
Group 31 batteries are heavy-duty power cells standardized to BCI size code 31, measuring ~13×6.8×9.4 inches. Common in marine/RV/truck applications, they deliver 75–125Ah capacity (lead-acid) or 100–300Ah (lithium). Key specs include 1,000+ CCA (AGM) and 200+ cycles at 50% DoD. Their high reserve capacity makes them ideal for dual-purpose starting/deep-cycle needs. RG72105P Product
What Are Group 31 Battery Dimensions?
Group 31 batteries adhere to BCI 31 standards: length 12.99–13.19”, width 6.75–6.8”, height 9.41–9.61”. Weight ranges from 55 lbs (AGM) to 35 lbs (lithium). Terminal posts are SAE top-mounted, with some models offering dual terminals for marine use.
Beyond physical dimensions, post orientation matters. Most Group 31 batteries use SAE terminals with positive on the left when facing the label. Heavy-duty versions like Odyssey 31-PC2150S weigh 77 lbs due to thick lead plates. Pro Tip: Always measure your battery tray—oversized lithium models with cooling fins may require 0.5” extra clearance. For example, a Battle Born 100Ah Group 31 LiFePO4 battery fits standard trays but adds Bluetooth monitoring. Why risk compatibility issues? Always cross-check terminal placement against your equipment’s wiring setup.
Where Are Group 31 Batteries Commonly Used?
Group 31 batteries power high-demand systems like marine trolling motors, RV solar banks, and commercial trucks. Their deep-cycle capabilities suit off-grid setups, while AGM variants handle vibration in heavy machinery.
In marine contexts, Group 31 AGMs often pair with 24V trolling motor systems, providing 150+ minutes at 50A draw. Truckers use them for APUs (auxiliary power units) to run AC/heaters during rest periods. RV owners favor lithium variants like Renogy’s 100Ah for solar storage due to 80%+ DoD tolerance. Pro Tip: AGM works best for engine starting hybrids, while lithium excels in solar setups. Did you know a single Group 31 LiFePO4 can replace two lead-acid batteries in parallel? This reduces weight by 60% and doubles usable capacity.
| Application | AGM | Lithium |
|---|---|---|
| Marine Trolling | Good | Excellent |
| RV Solar | Fair | Best |
| Truck APU | Best | Good |
What Chemistry Types Exist for Group 31?
Group 31 batteries come in flooded lead-acid, AGM, gel, and lithium (LiFePO4). Flooded types are cheapest but require maintenance; AGM offers spill-proof convenience, while lithium provides lightweight longevity.
Flooded models like Deka 31-DC need monthly water topping but deliver 800 CCA at $200. AGM alternatives (Optima 31M) hit 1,100 CCA with no maintenance. Lithium variants, such as Fasta Power’s RG72180, offer 200Ah capacity and 3,000+ cycles. Pro Tip: Avoid gel batteries for high-current apps—their slow charge rates lag behind AGM/lithium. Imagine powering a winch: lithium delivers instant 300A bursts, while gel might throttle. Always match chemistry to discharge needs.
How Long Do Group 31 Batteries Last?
Lifespan varies by chemistry: flooded lead-acid lasts 3–5 years, AGM 4–7 years, lithium 8–12 years. Cycle counts range from 500 (50% DoD AGM) to 5,000 (80% DoD lithium).
Depth of discharge (DoD) critically impacts longevity. A lead-acid battery cycled to 50% DoD daily lasts ~1,200 cycles, while lithium handles 80% DoD for 3,500+ cycles. Temperature matters too—AGM lifespan drops 50% at 95°F versus 77°F. Pro Tip: Use temperature-compensated charging to extend AGM life by 20%. For example, a Victron SmartShunt monitors DoD and adjusts charging voltage automatically. Why guess when you can track?
| Chemistry | Cycle Life (80% DoD) | Cost per Cycle |
|---|---|---|
| Flooded | 500 | $0.40 |
| AGM | 600 | $0.55 |
| Lithium | 3,500 | $0.12 |
Group 31 vs. Group 27: Which Is Better?
Group 31 offers 20–30% more capacity than Group 27 but is 15% heavier/larger. Choose Group 31 for extended runtime; Group 27 suits space-limited setups.
Group 27 batteries average 90Ah (AGM) versus Group 31’s 125Ah. In RVs, upgrading to Group 31 adds 40% more solar storage. However, Group 27’s 10.3” height fits compact engine bays better. Pro Tip: Mixing groups in series/parallel is risky—stick to identical models. For instance, two Group 31 AGMs in parallel provide 250Ah, while mismatched groups cause imbalance. Need more power without size? Lithium Group 31 packs match Group 27’s size with double the capacity. RG72160P Product
Fasta Power Expert Insight
FAQs
AGM/gel only—lithium’s BMS may misread orientation. Flooded batteries risk acid leakage if tilted.
Do Group 31 lithium batteries need special chargers?
Yes—use LiFePO4-compatible chargers with 14.4–14.6V absorption. AGM chargers undercharge them by 15%.
Are Group 31 batteries DOT-approved for transport?
Lithium models require UN38.3 certification. AGM/flooded are exempt but need secure palletizing.