Optima BlueTop Batteries for Marine and RV

Optima BlueTop is a sealed AGM (Absorbent Glass Mat) battery built for boats and motorhomes that need reliable engine starting and the ability to power accessories and trolling motors. Its spiral-wound construction resists vibration, is spillproof, and can be mounted in various orientations to fit tight compartments.

What It Is

BlueTop comes in two types: dual-purpose deep-cycle/starting (light gray case, model numbers begin with D) and starting-only (dark gray case, model numbers without the D). Dual-purpose models are suited to combined start and house loads; starting-only is for engines that don’t require deep cycling.

How to Choose Your BlueTop

• Choose D34M (compact dual-purpose) for smaller center consoles, campers, and lighter house loads.
• Choose D27M (mid-capacity dual-purpose) for 12V trolling motors up to ~55 lb thrust, small inverters, or weekend RV use.
• Choose D31M (maximum-capacity dual-purpose) for larger trolling motors, multiple electronics, fish finders, or longer anchoring.
• Choose 34M (starting-only, dark gray case) as a dedicated cranking battery when house loads are powered separately.

Tip: Match the battery Group size (34, 27, 31) to your tray dimensions and hold-downs. Verify terminal style and orientation before purchase.

Typical Models and Use Cases

The figures below are typical for the line; check current manufacturer specifications for your exact model.

Model	Type	Typical Use	Approx. CCA	Approx. Reserve Capacity
34M	Starting-only	Dedicated engine start for outboards/inboards	~800	~100 min
D34M	Dual-purpose	Start + light house loads/trolling	~750	~120 min
D27M	Dual-purpose	Start + moderate house loads/trolling	~800	~140 min
D31M	Dual-purpose	Start + heavier loads/longer runtime	~900	~155 min

Runtime Planning (Simple Estimates)

Reserve Capacity (RC) is the number of minutes a battery can deliver 25A before reaching 10.5V. You can approximate amp-hours and runtime:

• Estimate amp-hours (Ah): Ah ≈ 25 × (RC ÷ 60). Example: RC 120 → ~50Ah.
• Estimate runtime at load X: Hours ≈ (Ah × 0.5) ÷ X, assuming 50% depth of discharge for longer life.

Example: A D27M with ~140 RC → ~58Ah. A 25A trolling motor: runtime ≈ (58 × 0.5) ÷ 25 ≈ 1.2 hours to ~50% DoD. Lower speeds draw less current and extend runtime.

Charging and Maintenance

• Use a multi-stage charger with an AGM setting. Target absorption ~14.1–14.7V, float ~13.2–13.8V.
• Avoid sustained voltages above ~15V. Temperature-compensated chargers are recommended.
• For storage, fully charge, disconnect parasitic loads, and maintain above 12.6V. AGM self-discharge is typically low (about 2–3% per month at 77°F).
• Works well with solar charge controllers set to AGM profiles.

Installation and Safety

• Spillproof AGM can be mounted in various orientations; avoid fully inverted installs unless specified by the manufacturer.
• Secure firmly with a proper hold-down; BlueTop is highly vibration-resistant but must not move.
• Use correct cable gauge for your load/length and add a fuse or breaker near the battery positive.
• BlueTop marine models commonly provide dual terminals (SAE posts + 5/16" threaded studs). Verify clearance for both.
• Do not mix old and new batteries or different chemistries in the same bank.

Pros and Cons

• Pros: Dual-purpose capability, strong cranking, spillproof and vibration-resistant, low maintenance, flexible mounting.
• Cons: Lower usable capacity than similarly sized flooded deep-cycle or lithium options; higher upfront cost than flooded; requires AGM-compatible charging.

Good Fit vs. Not Ideal

• Use if: You need one battery to both start the engine and run moderate accessories or a trolling motor; you want a maintenance-free AGM that handles rough water or off-road travel.
• Avoid if: You routinely discharge deeply for many hours (consider multiple D31M, a true deep-cycle AGM bank, or LiFePO4), or you only need a starting battery (consider 34M starting-only).

Alternatives

• Flooded deep-cycle (marine): Lower cost, higher Ah per dollar; needs ventilation and regular maintenance.
• LiFePO4 (lithium): Much lighter with deeper usable capacity and fast charging; higher initial cost and requires a compatible charger/BMS.
• Optima YellowTop: Dual-purpose AGM often used in automotive/utility; for marine terminals and fitment, BlueTop is typically preferred.

Compatibility Notes

• Group sizes: Common sizes are 34, 27, and 31. Verify tray dimensions and height clearance.
• Banks and isolators: For start + house setups, use a battery switch or an automatic charging relay (ACR) to isolate and charge safely.
• Inverters: For inverters above ~600W, use D27M/D31M and short, heavy cables; consider parallel batteries.

FAQ

Is BlueTop a true deep-cycle battery?

The dual-purpose BlueTop (light gray case, D-models) handles regular cycling and engine starting. For very heavy daily deep cycles, choose the higher-capacity D31M, multiple batteries in parallel, a dedicated deep-cycle AGM, or LiFePO4.

Can I use a standard charger?

Use a charger with an AGM profile. Many modern “smart” chargers support AGM; verify voltage limits (about 14.1–14.7V absorption, 13.2–13.8V float).

Can I mount it on its side?

Yes. AGM is sealed and can be mounted in various orientations. Most installers avoid fully upside-down mounting.

Can I mix BlueTop with other battery types?

Mixing different ages, capacities, or chemistries (flooded, gel, lithium) in the same bank is not recommended. Keep banks matched for best performance and lifespan.

What size should I pick for a 12V trolling motor?

For light to moderate use, D27M is a common choice; for longer runtime or higher thrust, choose D31M or use two batteries in parallel. Check your motor’s amp draw and use the runtime formulas above to size correctly.