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Interstate SRM-4D Deep Cycle

Ideal replacement for Catalina Yachts house bank. Marine/RV replacement deep-cycle and cranking power battery. Amps: 1645 Cranking Amps: 1645 Cold Cranking Amps: 1314 30 Month warranty. 8.25" W x 21" L x 10.38" H. 117 lbs. Add $50 if you aren't returning a 4D core.

Product Code: Interstate SRM-4D

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$355.99 Interstate SRM-4D Special Order Item

CUSTOM: Interstate_SRM4D_Deep_Cycle.cfm

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Untitled Document


During the winter, should you lug those heavy batteries into the house? Will batteries freeze? How often should they be charged?

According to Raymond Toth of Swiftsure Marine Surveyors, battery storage temperature relies on specific gravity (the state of charge). A wet-cell battery is considered completely dead at 10.8VDC; a battery will freeze at -10C if it is at 11 VDC, but if fully charged at 12.8 it can withstand -45C.

Therefore, unless in extreme climates or left to discharge, batteries will likely only freeze if the batteries are old or defective, in which case they will need to replaced in any event. If you can charge them once every 2-3 months during the winter months, leave them aboard!

As well, heat can discharge your battery - so if you do bring them home, keep them in a cool place, periodically monitor their levels and top them up. The urban myth that a concrete floor will discharge your batteries is completely false. Happy winterization!

Trojan batteries are covered by a 1-year manufacturer's warranty. Most have a 36-month pro-rated warranty applicable after the 1 year.
In other words, your battery is 100% covered for one year. After that, the battery is covered for 3 additional years but at a diminishing value.

Trojan Battery Chart (measurements are imperial):

Type 20hr CCA Length Width Height Wet Weight
T105 6V 225   10 3/8 7 1/8 10 7/8 62
T125 6V 240 N/A 10 3/8 7 1/8 10 11/16 66
T145 6V 260 N/A 10 3/8 7 1/8 11 1/2 72
24TMX 12V 85 440 11 1/4 6 3/4 9 3/4 47
27TMX 12V 105 530 12 3/4 6 3/4 9 3/4 55
24-AGM 12V 80 440 10 1/4 6 5/8 9 1/2 52
27-AGM 12V 100 560 12 1/16 6 5/8 9 7/16 67
27TMH 115 620 12 3/4 6 3/4 9 3/4 61
SCS225 130 665 13 15/16 6 3/4 9 7/8 66


Types of batteries

Batteries on your boat handle two basic kinds of tasks, starting an engine and running electrical loads like lights, electronics and accessories for longer time periods. To choose a battery, first determine the battery’s application and then choose from one of the three battery chemistries: Flooded, Gel or AGM.

Starting Batteries: Starting batteries, which crank the starter of your boat’s engine, are the sprinters of your electrical system. They deliver between 75 and 400 amperes for 5-15 seconds, and then are recharged in short order by your engine’s alternator. Like all lead-acid batteries, they are constructed with alternating layers of negative and positive plates with insulation between them. Starting batteries have thinner and more numerous plates, providing extra surface area to generate high amperage bursts of current. The two drawbacks of this construction are that the plates are relatively fragile in high-impact environments, and that starting batteries do not tolerate deep discharges, which reduce their operating lifespan.

Deep Cycle Batteries: Your boat's House battery bank uses Deep Cycle batteries, the marathon runners of the storage system. They power the electrical loads on your boat when no charge source (shore power charger, engine alternator, wind generator or solar panel) is available. Consider them a kind of savings account into which energy is deposited or withdrawn.

Compared to starting batteries, which deliver high bursts of energy for short periods, deep cycle batteries recover fully after being heavily discharged over longer periods because their design features thicker plates with a high content of antimony. Overnight, their use might deplete 50-70% of the battery capacity, depending on the house loads of the boat. When the batteries are recharged, energy is re-deposited into the bank, and the process, or cycle, starts over.

Dual-Purpose Batteries: We generally advise that you choose either a deep cycle or starting battery for best performance and battery life, but dual-purpose batteries work well in some applications. With large thick plates containing more antimony than starting batteries and an active lead paste chemistry, dual-purpose batteries are a good compromise, tolerating deep discharges that would ruin a typical starting battery. Since they have lower storage capacity than comparably sized deep cycles, we recommend them for the following applications:

  • Runabouts or other small powerboats using a single battery for both starting and running loads with the engine turned off.
  • Sailboats with two identical batteries used interchangeably for starting and house electrical loads
  • Boats with one battery bank that does double duty for house applications and engine starting. Dual-purpose batteries will last longer and give more reliable service than a starting battery, for about $20 more per battery.

What to look for

Starting functions: The amount of power available for cranking a starter is measured several ways:

CCA vs. MCA: The two common power measurements are CCA (Cold Cranking Amps, the number of amps a battery can deliver for 30 seconds at 0°F while maintaining its voltage above 7.2 volts) and MCA (Marine Cranking Amps, similar but measured at 32°F instead of 0°F). The reason that MCA are 20-25% higher than the CCA is because batteries work better at higher temperatures.

Reserve Minutes indicate how long a battery can sustain a load of 25 amps before it drops to 10.5 volts. A battery rated at 150 minutes can operate a 25A load for 2 1/2 hours. Starting batteries aren’t used to handle loads for long periods, so reserve minutes are less critical.

Size: Engine size, type, and ambient temperature determine what size cranking battery you need. High cranking power (and a larger battery) is required for cold temperatures, diesel engines, or large and high compression gas engines. If a Group 24, 550 CCA battery worked well for five years, we’d recommend replacing it with a similar model. If, however, it cranked too slowly, or failed after a season or two, we’d suggest that you look for a battery with a higher CCA or MCA rating.

Deep Cycle Functions

Battery Capacity measurements are commonly expressed in Amp-hours (Ah) and Reserve Minutes. Amp-hours measure the total amount of energy that a battery can deliver for 20 hours at a constant rate of discharge, before the voltage drops to 10.5 volts. This means that a 200Ah battery can run a 10A load for 20 hours. The reserve minute rating is the number of minutes that a battery can run a 25A load until dropping to 10.5V, just like with starting batteries. A Group 27 deep cycle battery with a rating of 180 reserve minutes will run a 25A load for three hours. House loads range from 5A to 25A or more. Ah is generally the more relevant measurement for house banks.


Battery manufacturers measure longevity by discharging full batteries until their voltage drops to 10.5 volts. The batteries are recharged under controlled conditions, and the process is repeated until the battery fails to hold half of its rated capacity. This measurement, called cycle life, shows how many discharge cycles a battery provides over its lifespan. This ability to cycle repeatedly is what differentiates deep cycle batteries from starting batteries, which can’t withstand more than a few deep discharges before they begin to fail. If nothing else, cycle life provides a baseline for comparing one battery to another.

Choose the right battery chemistry

Marine batteries are available in three chemical types: flooded, Gel and AGM (Absorbed Glass Mat). Which type you choose is based on your needs (deep cycle vs. starting), the capacity and lifespan you are looking for, and your budget.

Flooded batteries, unlike other types, use a reservoir of liquid sulfuric acid to act as a pathway between positive and negative plates, which produce hydrogen and oxygen when the battery is being charged. Vented wet cell batteries allow the gases to escape into the atmosphere, unlike gel and AGM batteries, which recombine the gases and re-introduce them to the system. Vented hydrogen is an explosive gas, so battery boxes and compartments must be vented to let the gas escape safely outside the boat. Flooded deep-cycle batteries require maintenance-periodic inspection and topping-off with distilled water.

Flooded batteries handle overcharging better than gel and AGM batteries, because of this hydrogen venting and because they are not sealed like the other types. They self-discharge at a higher rate (6 to 7% per month) and thus require off-season charging. Wet cells must be installed in an upright position and do not tolerate high amounts of vibration. Their initial cost is lower than similarly sized AGM or gel batteries. Properly charged and maintained, our premium wet cell deep-cycle batteries are capable of between a few hundred and over a thousand discharge cycles, which can translate to many years of dependable service.

Gel Batteries: The SVR design nearly eliminates gassing, so they are safer to install around people and sensitive electronics (but gel and AGM batteries still need to be vented). Gel batteries are manufactured to very high standards of quality and consistency, since it is not possible to add water or gain access to the interior. The "gel" is a combination of sulfuric acid, fumed silica, pure water and phosphoric acid. After mixing during manufacturing to a thin liquid form, it is sucked into each cell by vacuum pressure up to six times, eliminating voids and air pockets on the plates that would cause dead spots and reduce performance. Once it is in place, the gel becomes quite viscous, which prevents leaks if the battery is inverted or the case is damaged.

Charging causes a small amount of hydrogen and oxygen to be generated at the plates, like a flooded battery, but the pressure inside the cells combines the gasses to create water (so they are called "recombinant" batteries). This keeps the battery from drying out due to charging, but it also requires that the vessel’s charging system be very carefully regulated to prevent high voltage over-charging.

AGM batteries: Sealed Valve-Regulated AGM (Absorbed Glass Mat) batteries feature fine, highly porous microfiber glass separators compressed tightly between the battery’s positive and negative plates, which are saturated with just enough acid electrolyte to activate the battery. During charging, precision pressure valves allow oxygen produced on the positive plate to migrate to the negative plate and recombine with the hydrogen, producing water. In addition to providing equal saturation across the entire surface of the battery’s positive and negative plates, the fibers in the dense glass mats embed themselves into the plates’ surface like reinforcing rods in concrete, providing more plate support and better shock and vibration protection than in conventional batteries.

High-density AGM batteries have lower internal resistance, allowing greater starting power and charge acceptance, and quicker recharging than other types of deep cycle batteries. High acceptance means that AGM batteries can accept the highest charging current, up to 40% of the amp hour capacity of the battery, compared to about 25% for the other two battery chemistries. Long life, a low 3% self-discharge rate and outstanding performance make AGM batteries excellent dual-purpose batteries for boaters who require quick starting power and reliable deep cycle ability.

Battery tips for best performance

No matter what kind of battery chemistry you choose, follow these recommendations to get the best performance:

  • Stay with one battery chemistry (flooded, gel, or AGM.) Each battery type requires specific charging voltages. Mixing battery types can result in under- or over-charging. This may mean replacing all batteries on board at the same time.
  • Never mix old batteries with new ones in the same bank. While it seems like this would increase your overall capacity, old batteries tend to pull down the new ones to their deteriorated level.
  • Regulate charge voltages based on battery temperature and acceptance (manually or with sensing) to maximize battery life and reduce charge time. Ensure that your charging system is capable of delivering sufficient amperage to charge battery banks efficiently. This generally means an alternator with 25% to 40% as many amperes as the capacity of your entire battery bank.
  • Keep batteries clean, cool and dry.
  • Check terminal connectors regularly to avoid loss of conductivity.
  • Add distilled water to flooded lead acid batteries when needed. Keep them charged. Leaving them in a discharged state for any length of time will damage them and lower their capacity.
  • Clean corrosion with a paste of baking soda and water.

Need more juice?
If your boat came from the factory with only one battery, or with two batteries of inadequate size, consider installing a second battery bank. Boats often need two banks to have a second "reserve" bank to be sure the engine will start, or to have a large "house" bank so you can run bigger DC loads for longer time periods. If you are installing a reserve starting battery, you can usually ensure enough amps of cranking power by duplicating the type and size of your original battery. To install a "house" bank, you should probably invest in a quality deep cycle battery.

Marine Batteries
Starting batteries are similar to automotive batteries. They can supply lots of current for a short period of time, but like to be recharged almost immediately and are not tolerant of deep discharges. They are appropriate as the single battery for ski boats, runabouts, personal watercraft, and other boats with minimal DC loads where the engine is always running.

Deep–cycle batteries can endure repeated deep discharging and recharging without damage. They are appropriate for sailboats, fishing boats, and all other boats with larger DC power requirements. Any battery used to power onboard DC loads (lighting, trolling motors, inverters, etc.) should be a quality deep–cycle battery, like our SeaVolt brand.

Safety Precautions

  • Batteries contain a tremendous, and potentially dangerous, amount of stored energy. Whenever you are working on your electrical system, remove the positive battery cables from the battery terminals to eliminate the chance of a short circuit and/or possible electrocution.
  • The American Boat and Yacht Council (ABYC) publishes safety standards for circuit protection, wire sizes, and other related issues in electrical systems. Where appropriate, we have provided information on circuit breakers and wire sizes which are in accordance with these guidelines. The complete text of these standards is available in reprints from the ABYC.
  • Since the connections made in the battery circuits can conduct hundreds of amps, it is imperative that you have low resistance connections. This means having clean metal–to–metal connections, the right size terminals which are properly crimped and waterproofed, and secure mechanical fasteners.
  • For outboard engine applications we recommend replacing wing nuts on the tops of the battery with nylock nuts or hex nuts and lock washers that are tightened to at least 10 foot pounds of torque. For inboard engine applications you should use clamp–on battery terminalsconnected to the correct gauge of battery cable.
  • Be sure to wear safety glasses when working on batteries and have a water hose or other available method of flushing battery acid out of the eyes and off the face. Be careful of using un–shielded droplights or any open sources of heat or flame around the batteries. Be very careful with uninsulated tools that might short across the battery terminals.

Location, location and location
This credo works as well for batteries as it does for real estate. Batteries are temperature sensitive, needing a temperature that is comfortable for a person, and high temperatures dramatically shorten their life. If the proposed battery location is too hot for you, it is also too hot for your battery. This presents a dilemma for many battery installations, since you want short runs of battery cable to your engine’s starter or alternator to prevent a loss of voltage, but your battery won’t last long in a hot engine room and must be ventilated. Batteries, especially the flooded type, give off lighter–than–air explosive hydrogen gas when charging, so they must be vented from the top directly to the outside of the boat. If there is not sufficient natural ventilation you may have to add a sparkproof exhaust fan to eliminate gas buildup and to lower the temperature. Batteries, especially the flooded type, must also be easy to service.

Use quality battery cables
We recommend low–resistance, tinned copper wire in all applications. Moisture, vibration, heat, abrasion, and chemicals are major enemies of all electrical system components, and only marine rated wire (like that from Ancor Marine) is built to withstand these conditions. Be sure to use tin plated copper connectors as well, for the least electrical resistance and the best corrosion protection. We recommend double crimped terminals, with solid metal–to–metal connections and heat shrink tubing for waterproof protection.

Pre–manufactured battery cables are available in various lengths with well–constructed connectors, properly covered with adhesive–lined heat shrink and terminated with closed barrel ring terminals. However, the lengths available may not be appropriate for your installation so you may have to make your own battery cables. To do this requires a proper crimper. There is no way to shortcut this, since terminals smashed on the cable with a pair of Vise Grips or a few hammer blows will certainly fail, perhaps with catastrophic results. You must use a heavy–duty crimper designed for the purpose. Use closed–barrel terminals with holes the right diameter for the bolts to be used at the terminations. Positive and negative terminals often have different diameters. Spray a corrosion inhibitor such as Fluid Film, Lanocote, or Boeshield into the connector before crimping. Cover the joint between the cable insulation and the connector body with a three–inch section of adhesive–lined heat shrink tubing. Using a heat gun is the best way to apply heat shrink, although you can use a propane torch with a flame spreader if you are very careful. Be sure to have a fire extinguisher on hand. You can also tape the joint with several layers of quality electrician's tape and finish it with a small nylon tie where the tape ends to keep it from un–wrapping due to heat and solvents. Remember to cover positive terminals with a boot (or the battery box cover) to prevent shorting.

Battery Boxes
The batteries must be secured so there is no more than one inch of movement in any direction. A loose battery skidding about (weighing about 3/4lb per amp hour, or 150lb for a 200Ah battery) is both a physical hazard and a fire hazard. Pre–manufactured acid–proof battery boxes, available in various sizes, are the best way to safely anchor the batteries. Use more than one box if your batteries require you to make a series or parallel arrangement. Home–built battery boxes must be ruggedly constructed from marine grade plywood, covered inside and out with fiberglass cloth saturated with several coats of epoxy, and secure even in the event of a capsize. Do not mount batteries directly above or below a fuel tank, fuel line or filter, or directly below battery chargers or inverters.

Battery Switches
Old–school OFF–1–2–BOTH battery switch: Most single engine boats built in the last 30 years are equipped with two nearly identical (and undersized) marine batteries, used interchangeably for starting or house loads. Prior to starting the engine, the operator would turn the OFF–1–2–BOTH battery switch to the BOTH position to have both batteries' full cranking power. With the engine now running, the switch would stay in the BOTH setting, and both batteries would be charged while powering to the day’s destination. Once the engine was turned off (while anchored or under sail) the operator would (in theory) return the switch to the 1 or 2 position, and reserve a battery for starting. When it was time to crank the engine again, the battery switch would be turned to BOTH, or possibly to the reserve battery, and the engine would be started.

The problem is that this requires a lot of thought by the operator, who is trying to relax in the first place. Inevitably, the operator (or the operator’s Brother in Law) may leave the switch in the BOTH position, resulting in a very dead battery. Statistically, dead batteries are one of the most common reasons for calling a towing service. "I can’t crank my engine!"is right up there with "I’m out of gas!" for ruining a day on the water

Dual Circuit Plus™: A simpler alternative to isolate your Start and House circuits is available in the Dual Circuit Plus Battery Switch (Model 7808801) . In the ON position, it keeps your batteries isolated, so both can't be fully discharged by accident. In the COMBINE position, it parallels your batteries in the event of a low Starting battery. Used with the BatteryLink ACR, it automatically combines or isolates your batteries when in the ON position.

The most affordable way to purchase the Dual Circuit Plus switch and SI7610 ACR is to buy a kit that includes both, the “Add–a–Battery” Dual Circuit System, Model 8646275.

Charge Management
Battery Isolators used to be the best method of distributing charging current to multiple battery banks while assuring that they remain electrically isolated during discharge. These devices are electrical "one–way check valves" that allow current to flow to, but not from, the battery. Their disadvantage is that diodes cause a voltage drop that wastes charging energy, creates heat and causes batteries to be undercharged. Alternators with external voltage sensing can correct for the undercharging problem, but voltage drop and the heat generated remain a problem.
Automatic Charging Relays (ACR) are becoming a popular method for achieving the same goal as isolators, but they work on a different principle. Instead of using diodes to block current from flowing in both directions, ACRs use mechanical relays combined with a circuit that senses when a charging source is being applied to either battery. When a charge is being applied, the ACR closes; and when the circuit senses that the charge is no longer present, the ACR opens (after a short time delay to assure that the ACR doesn’t open due to temporary voltage sags caused by load startups, like a refrigerator turning on).

Automatic Charging Relays have lots of other uses in addition to isolating the Start and House batteries, and Blue Sea Systems now produces two relays for two kinds of jobs:

  • CL7600 Current Limiting: Great for automatically charging a remote battery for a windlass or bow thruster, for combining or isolating two banks on a smaller outboard, I/O or inboard. Connect it to your high–powered stereo to prevent the subwoofer system from draining the House bank. Handles 60 continuous amps. User–adjustable open and close voltage settings, for 12V systems. Includes Current Limiting feature.
  • SI7610 Starting Isolation: Designed for isolating a larger House battery, and rated for 120 continuous amps. Allows temporary isolation of house loads from engine circuit during engine cranking to protect sensitive electronics. Waterproof rated IP67. 12/24V systems.
  • ACRs can be used for load shedding, pilot house navigation battery isolation, and charge current limiting for a remote battery. See www.bluesea.com for detailed technical papers.

Adding another battery is a good idea if you want to add a powerful stereo subwoofer system, cabin lighting, electric windlass, wakeboard ballast pump or any of the other electrical and electronic accessories we all want. The installation can be as simple as connecting two batteries in parallel to make one larger battery bank. You can build in redundancy and failure protection with two battery banks, battery switches and charge management devices like ACRs. That way, when you drop anchor and use all your new gadgets, your engine will still start at the end of the day.

Remember that you must match battery chemistries between your banks. If your starting battery is of the lead–acid type, stick to a deep cycle battery of the same chemistry, instead of choosing a gel or AGM battery with different charging requirements.


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