What Is A 4D Battery?
A 4D battery is a large, heavy-duty lead-acid or AGM battery classified by its Group 4D size (approx. 20.75″L x 8.75″W x 10″H). Designed for deep-cycle applications, it provides 150–220Ah capacity at 12V, ideal for RVs, marine systems, and industrial equipment requiring sustained power. AGM variants offer spill-proof operation and vibration resistance, while flooded types are cheaper but require maintenance. Pro Tip: Use reinforced trays—4D batteries often weigh 120–150 lbs.
What are the key specifications of a 4D battery?
4D batteries feature 20.75″ x 8.75″ x 10″ dimensions and 12V output, delivering 150–220Ah via thick lead plates. AGM models operate at 100–120Wh/kg energy density, while flooded types average 80Wh/kg. Terminals are typically SAE post or L4 studs. Weight ranges 125–150 lbs—40% heavier than Group 31 batteries. Pro Tip: Always verify terminal orientation; some marine models use reverse polarity.
Beyond physical specs, 4D batteries excel in deep-cycle performance, enduring 500–800 cycles at 50% depth of discharge (DoD). AGM versions charge faster (0.2C vs. 0.1C for flooded) and tolerate -40°F to 140°F. For example, a 200Ah AGM 4D battery can power a 2,000W RV inverter for 1 hour at 80% efficiency. However, why do some users prefer flooded lead-acid despite maintenance needs? Lower upfront cost—$300 vs. $600 for AGM—makes them viable for budget-conscious projects.
| Spec | AGM 4D | Flooded 4D |
|---|---|---|
| Cycle Life | 800 cycles | 500 cycles |
| Charge Rate | 20–40A | 10–20A |
| Maintenance | None | Monthly water checks |
Where are 4D batteries commonly used?
4D batteries dominate marine/RV house banks, telecom backup systems, and off-grid solar storage due to high capacity. Their vibration-resistant design suits heavy machinery like forklifts. AGM variants are preferred for boats where tilt risk exists. Pro Tip: Pair two 4D batteries in parallel for 24V systems—ensuring matched age/capacity avoids imbalance.
Practically speaking, 4D batteries power energy-hungry devices like RV air conditioners (1,500W) for 2–3 hours or fish finders for 8+ hours. In marine contexts, they handle bow thrusters and winches requiring 300–500A surges. But what if space is limited? Some users opt for lithium 4D replacements—50% lighter but 3x pricier. For example, a 12V 200Ah lithium 4D battery weighs 70 lbs vs. 130 lbs for AGM, ideal for sailboat keels.
How does a 4D battery compare to Group 31 or 8D?
4D batteries offer 20–30% more capacity than Group 31 (100–125Ah) but are 25% smaller than 8D (225–325Ah). While 8D suits industrial loads, 4D balances size/power for mid-tier applications. AGM 4D cycles 2x longer than Group 31 flooded. Pro Tip: Use battery dimension templates—Group 31 is 13″ long vs. 20.75″ for 4D.
In real-world terms, upgrading from Group 31 to 4D adds 50Ah—enough to run a 12V fridge for 10 extra hours. However, 8D batteries might overkill for most RVs, adding unnecessary weight. Why choose 4D over lithium? Initial cost: a 200Ah AGM 4D costs $600 vs. $2,000+ for lithium. But lithium lasts 3x longer—making ROI positive after 5+ years.
| Feature | 4D | Group 31 | 8D |
|---|---|---|---|
| Capacity (Ah) | 150–220 | 100–125 | 225–325 |
| Weight (lbs) | 125–150 | 70–80 | 150–175 |
| Typical Use | RV/Marine | Truck/Trailer | Industrial |
Fasta Power Expert Insight
FAQs
Yes—4D batteries with 800–1000 CCA (cold cranking amps) can start mid-sized diesel engines. Opt for dual-purpose AGM models balancing cranking/deep-cycle performance.
How long does a 4D AGM battery last?
5–7 years with proper charging (13.8–14.4V) and ≤50% DoD. Avoid storing below 12.2V—sulfation permanently reduces capacity.