The Blue View - Latest & Greatest Batteries - Part 4

battery bank So, after all that, what’s the best battery for our application? Let’s start by comparing the true cost of each battery type over its life.

To recap our assumptions:

  • Recharge cycles: We will need to recharge 200 times a year – from 50% DOD to 80% DOD
  • Recharge cost: It costs us $3.50/hr to run the engine, and the alternator puts out 110 amps at that speed
  • Battery capacity: We have roughly 800 ah in our house battery bank

Since no engineering analysis is complete without at least one spreadsheet…

Actual Cost of Each Battery Type

Battery Type

Initial Cost

Expected Life in Years


$/Year Recharging

$/Year Maintenance

Total $/Year











































Lithium Ion







Some surprising results…

  • Given our kind of usage, the flooded lead acid is actually the most expensive, even though it is the least expensive to buy. Obviously, if we weren’t on the hook as much or had a less expensive method of recharging, the results would be totally different.
  • The Lithium-Ion, even though it costs significantly more initially, falls in the middle of the cost range.

Deciding which one…

Starting with the ones I’m ruling out:

  • Flooded lead acid because of the total cost and all the maintenance that’s required
  • Gels because they can’t be equalized and are the heaviest and most expensive of the remaining candidates
  • Spiral Wound because they can’t be equalized, have the least technical information available, and seem to only be available in smaller battery sizes

Of the remaining candidates, all are viable candidates for our application. Here are a few further thoughts:

  • Carbon foam seems the best candidate, but I am somewhat reluctant because of the limited track record – and anyway, they are on back-order with no information regarding shipping date.
  • Lithium-Ion look quite good, but the upfront cost is painfully high
  • Leaving TPPL and Lifelines… both good quality batteries, and I think I’ll be happy with either.

The Blue View - Latest & Greatest in Batteries - Part 3

battery bank There are two criteria I’ve included, which will be helpful when comparing the batteries for our application. One is the recharge time from 50% DOD to 80% of full charge and from 50% DOD to full charge. The time we spend running the engine every day to recharge the batteries is an important consideration. I’ve also included an estimate of the time spent each month on maintenance. Given how I routinely mistreat them, even the ‘maintenance free’ batteries require some attention each month, whether it is something as simple as giving them a full charge or performing a full equalization on a routine basis.

Flooded Lead Acid Batteries. These are similar to the batteries that have been used in cars for the last 100 years, but these are designed for deep discharging. The biggest advantage they hold is their inexpensive price – comparatively speaking. These are vented batteries - as they are charged, the water boils off, so the water level should be checked frequently, as should the specific gravity. They are also subject to sulfation and stratification, thus as they age, they should be equalized every month or two. The charging rate is low – the Rolls batteries set the maximum bulk charge rate at 15% of the total 6 hour amp-hour rating, so for an 800 ah battery bank, the maximum bulk charge would be 90 amps. Using their formulae, it would take a total of 7.2 hours to fully recharge a battery bank that was at 50% DOD. On the other hand, they are fully warranted for 2 years and have a seven-year pro-rated warranty.


  • Inexpensive
  • Good life expectancy if properly maintained


  • A lot of maintenance
  • Will spill acid if knocked over (or the boat is knocked down or capsized)
  • High rate of self-discharge
  • Low charge rate
  • Batteries will release hydrogen gas while charging, so battery compartments must be vented.
  • Heavier than other technologies

Manufacturers: Trojan, Exide, Surrette, U.S. Battery

Weight: 110-115lb (50-52kg) per 200 ah

Recharge Cycles: 1000-1500, if properly maintained

Recharge time: 50% to 80% in 2.7 hours; 50% to Full Charge in 5.7 hours

Monthly maintenance time estimate: 12-14 hours, including a monthly equalization

Expected Life: 5-7 years

Cost of Batteries: About $1.30/ah - Four batteries totaling 820 ah: $1080

Gel. Gel Cell batteries suspend the electrolyte in a paste-like gel, which allows electrons to flow but will not leak if the battery is tipped over or the case is broken. They are leakproof and even submersible. They have a high number of recharge cycles and are maintenance free – in fact, they cannot usually be equalized. The recharging cycle must be very carefully regulated and requires a smart charger. The cost is fairly high.


  • No maintenance
  • Leakproof
  • High number of recharge cycles


  • Relatively high cost
  • Charging must be carefully controlled
  • Heavy

Manufacturers: Trojan, Deka (Deka/MK produce privately labeled batteries for several other companies)

Weight: 155-165 lb (70-75 kg) per 200 ah

Recharge Cycles: 600-1000 if properly recharged

Recharge time: 50% to 80% in 1.1 hours; 50% to Full Charge in 3.6 hours

Monthly maintenance time estimate: 4 hours – at least one full charge a month

Expected Life: 5-6 years

Cost of Batteries: About $3.50/ah – Four batteries totaling 900 ah: $3180

AGM. Absorbent Glass Mat (AGM) batteries consist of negative and positive plates sandwiched between layers of glass mat. There is no liquid acid to spill and the battery is sealed with pressure relief valves that prevent venting of hydrogen gas under normal circumstances. There are several different versions of AGM batteries, but four products are of particular interest: Lifeline, TPPL, Spiral Wound and Carbon Foam. I’ll talk about each below:

Lifeline AGM. The Lifeline AGMs we’ve had for almost eight years now have obviously served us well. They are quality made and designed for deep cycle applications.


  • Maintenance free
  • Very fast max recharge rates (up to 5c)
  • Moderate price
  • Good life if properly maintained
  • Long shelf life – slow self-discharge rate
  • Can be equalized


  • Heavy
  • Must have a charge rate of at least .2c to obtain max number of cycles (min of 160 amps for an 800ah bank);
  • Requires periodic equalization if not routinely returned to full charge regularly

Recharge Cycles: 1000

Recharge time (max charge rate): 50% to 80% in 8 minutes; 50% to Full Charge in 2.5hrs

Recharge time (200 amp alternator and 800ah bank): 50% to 80% in 1.2 hours; 50% to Full Charge in 5.7 hours

Monthly maintenance time estimate: 10-12 hours – at least one full charge/month plus an equalization quarterly

Expected Life: 6-8 years

Cost of Batteries: $3.11/ah – Four batteries totaling 820ah: $2650

TPPL. The plates in the Thin Plate Pure Lead (TPPL) AGM batteries are, as the name suggests, constructed of 99.99% pure lead rather than a lead alloy. The manufacturer claims this allows them to utilize thinner plates and to insert more of them in the same space, effectively increasing plate area.


  • High number of cycles, and a very high recharge rate, up to 3.1c
  • Like most AGMs, they also have a slow self-discharge rate
  • Maintenance free and non-spillable


  • Must have a high recharge rate (.4c) to optimize cycle life

Manufacturers: Odyssey, Northstar

Recharge Cycles: 700-800

Recharge time (max charge rate): 50% to 80% in 6 minutes; 50% to full charge in 10 minutes

Recharge time (200 amp alternator and 800ah bank): 50% to 80% in 1.05 hours; 50% to Full Charge in 4.0 hours

Monthly maintenance time estimate: 6 hours – one full charge per month

Expected Life: 4-5 years

Cost of Batteries: $2.90/ah – Eight batteries totaling 800ah: $2300

Spiral Wound. These batteries also use plates constructed of 99.99% pure lead, but the thin lead plates are made of a continuously cast strip wound in a spiral. A glass mat is wound alongside the plate, forming sort of a jelly roll. The glass mat serves to insulate the plates and to provide a means of suspending the electrolyte. The manufacturers of these batteries don’t seem to want to provide a lot in the way of comparative specs, like recharge cycles, equalizing, etc. so I have provided estimates below.

spiral wound batteries


  • High initial charge rate
  • Slow self-discharge rate
  • Sealed and non-spillable


  • Must charge a long time to reach full charge;
  • No equalization,
  • Recharge cycles will be less without routine full charges

Manufacturers: Optima, Yuasa, Exide

Recharge Cycles: 300-400

Recharge time (max charge rate): 50% to 80 in 1.05 hours; 50% to full charge in 6-8 hours

Recharge time (200 amp alternator and 800ah bank): 50% to 80% in 1.05 hours; 50% to Full Charge in 6-8 hours

Monthly maintenance time estimate: 8 hours – one full charge per month

Expected Life: 4 years

Cost of Batteries: $2.97/ah – Ten batteries totaling 775ah: $2230

Carbon Foam. A few years ago, Caterpillar developed a new battery technology that was intended for their heavy equipment. They embedded a carbon foam grid onto the internal negative plates of an AGM battery. This grid prevents large sulfate crystals from forming, making it more suitable for deep discharge cycling. They spun the division off, and after a few false starts, the OceanPlanet Energy/Bruce Schwab company obtained the rights and now builds and markets the technology as the Firefly Oasis battery. Practical Sailor and Nigel Calder both put it through its paces with good results. It hasn’t been out long enough to do any long-term testing, but the short-term testing was quite positive. It has a large number of charge cycles and can be partially recharged indefinitely without affecting its long-term performance – an important feature.

carbon foam


  • High number of cycles, and a high recharge rate, up to 2.5c
  • Like most AGMs, they also have a slow self-discharge rate
  • Maintenance free and non-spillable
  • Can be routinely operated at between 50% charge and 80% charge without affecting performance


  • More costly than other AGMs

Recharge Cycles: 3600 at 50% DOD

Recharge time (max charge rate): 50% to 80% in 1 hour; 50% to full charge in 3 hrs (estimate)

Recharge time (200 amp alternator and 800ah bank): 50% to 80% in 1.25 hours; 50% to Full Charge in 3.5 hours (estimate)

Monthly maintenance time estimate: 2 hours – one restoration charge per quarter

Expected Life: 10 years

Cost of Batteries: $4.86/ah –Seven batteries totaling 812ah: $3400

Lithium-ion. There are several lithium-ion based batteries, and some, like the Samsung Galaxy Note 7 have garnered a lot of negative publicity. The type of lithium-ion battery used in cell phones is Lithium-Cobalt-Oxide, which has a very high energy density. If it is charged at too high a rate or if the outputs ever short, however, the battery will overheat, possibly resulting in a fire or even an explosion. The type used in our application is a Lithium-Iron-Phosphate battery, which has a lower energy density, but is also much more stable and economical. Even though it is more stable, however, a battery monitoring system must be provided which will prevent the cells from overheating, overcharging, discharging too quickly, or becoming totally discharged.

lithium ion battery


  • Lightweight
  • Fast charge rate
  • Large number of recharge cycles
  • Large usable capacity – 80% of capacity vs. 50% of lead acid
  • Can be routinely operated at between 50% charge and 80% charge without affecting performance.


  • Expensive
  • Requires battery monitoring system

Recharge Cycles: 3000-5000

Recharge time (max charge rate): 50% to 80% in 1 hour; 50% to full charge in 2 hrs

Recharge time (200 amp alternator and 800ah bank): 50% to 80% in 1 hours; 50% to Full Charge in 2 hours

Monthly maintenance time estimate: 2 hours – one full charge per month

Expected Life: 10 years

Cost of Batteries: $11.54/ah – Three batteries totaling 780ah: $9000

So, after all that, what’s the best battery for our application? Stay tuned until tomorrow for the exciting conclusion.

The Blue View - Latest and Greatest in Batteries Pt. 2

battery schematic Boat batteries come in two basic types – starter batteries and house batteries. Starter batteries are designed to provide very large, short term current as the engine is started, then are recharged while the engine is running. These batteries are usually rated by their Cold Cranking Amps (CCA) - a measure of how many amps of current the battery can put out over a 30 second period without discharging the battery. For example, a battery with a CCA rating of 500 amps can provide 500 amps of current over a 30 second period in freezing temperatures and still maintain a voltage of at least 7.2 volts.

House batteries, on the other hand, are used to provide power for all the electrical equipment aboard, from the refrigerator to the laptop computers, and need to be recharged periodically. These batteries are designed to provide a much smaller current over a longer period than are starter batteries, and are rated by the number of amp-hours (ah) they can provide over 20 hours. Thus, a 200 ah battery can provide a constant 10 amps of current over a 20 hour period before becoming fully discharged.

The house batteries on Nine of Cups live most of their lives somewhere between ½ and ¾ full charge. Over the course of a day or two, the electrical demands of the boat slowly discharge them, but before they reach 50% of their full charge, we start the engine for an hour or two to recharge them. This never fully recharges the batteries – it would take several hours to totally top them off – but it does restore them to about 80% of full charge.

Almost every battery manufacturer will tell you this is a bad way to treat their batteries. They should always be recharged to full charge; otherwise the battery life will be much shorter than their normal expected life. Unfortunately, in the real world, this is how cruising sailboat batteries get treated. With our current Lifeline AGM batteries, I partially compensate for this mistreatment by running the engine long enough to fully recharge the battery bank at least once a month. In addition, after the first year or two, I found I needed to equalize the batteries once a quarter. (Equalizing is essentially a very controlled overcharging process that helps remove any sulfation build-up.) In evaluating batteries for a cruising boat, it’s important to consider how mistreating the batteries will affect the battery life, and the cost and time involved in compensating for the abuse they receive.

life line

Since our house batteries are now about 8 years old (that’s about 120 in battery years), I am on a quest to find the best, most cost effective replacement batteries for Cups. So, what are my criteria for the ideal battery? Here is what I think is important – not necessarily in order of importance:

  • Long life. Most battery manufacturers provide an important spec – how many times the battery can be recharged before it begins to lose its capacity. Usually, this is a function of how deeply discharged the battery is between recharges. A battery may be rated for 300 recharge cycles if it is always allowed to discharge to 25% of full capacity (Depth of Discharge or DOD) or 450 cycles if it is routinely recharged at 50% DOD (which is why we never let our house batteries discharge below 50% DOD). The more recharge cycles a battery is rated for, the longer its life will be. Depending on the battery type, the number of recharge cycles ranges from 100-200 cycles for an inexpensive battery to well over 4000 cycles for an expensive Li-Ion battery.
  • High charging rate. The higher the charging rate, the faster a battery can be recharged and the fewer hours I’ll need to run the engine. This assumes, of course, that the charger – whether it is an alternator or a battery charger – can provide sufficient amps to take advantage of a high charge rate. An 800 amp-hour battery bank being charged by a 100 amp alternator won’t charge all that fast no matter what the maximum charge rate of the battery.
  • Low actual cost. Obviously, the less they cost the better, but the true cost of a battery bank is much more than the initial purchase price. What does it cost to maintain them? How about the cost to keep them charged? What is the expected life? A battery that costs $250, but only lasts 2 years is more expensive over its life than a battery that costs $400, but lasts 6 years. There’s also the cost in time, effort and dollars, to swap out those four, 150 pound batteries, and recycle them – you can’t just toss them in the dumpster.
  • Low maintenance. How much time is required to keep them maintained and to compensate for my mistreatment of them? Do I need to check acid levels every few weeks? Equalize them once a month?
  • High level of safety. All batteries present safety issues. Wet cell lead acid batteries will boil off explosive hydrogen gas if overcharged and can spill acid if tipped over – both of which are possibilities on a sailboat. Sealed Gel and AGM batteries can generate hydrogen gas or can catch fire and burn if overcharged or charged at too high a rate. And we’ve all heard about the fire hazards lithium batteries pose if recharged incorrectly or are ruptured. All batteries present a risk of burns or fire if the terminals are shorted. So, in my mind, while there is no totally risk free battery, the ideal battery would be one that presents the least danger to the boat and crew.

There are a couple of additional things to consider before deciding on which batteries to buy. The first consideration is how many batteries are needed and how large they need to be. The process for determining this is to evaluate our electrical consumption over a 24-hour period. I’ll devote a future blog to this topic, but for now, we’ll assume our daily power usage averages 180 amp-hours. A good rule of thumb is to have a minimum of 3-4 times the daily electrical consumption in battery capacity, so we need batteries with a total capacity of at least 540 to 740 amp-hours.

Another very important consideration is how the boat is used. A sailboat that is used seasonally, maybe taken out for a couple of weeks during the summer and a dozen weekends throughout the year has much different requirements than a full-time cruising boat that spends very little time with shore power. In the first case, the batteries only see 10-20 recharge cycles every year, and even the least expensive batteries will last many years. In the latter case, the batteries may see 200-300 recharge cycles each year, and the less expensive batteries will likely only last a year or two. Thus, the ideal battery for one boat may not be the ideal battery for every boat.

So, let’s make some assumptions and estimates regarding our batteries to help in the selection process.

  • Daily Power Consumption. We calculated our average daily power consumption to be around 180 amps. Some days will be considerably more (when we’re passagemaking and running nav instruments and the autopilot, for example), and some days less (when we’re ashore most of the day and not spending hours on the computers, writing blogs).
  • Capacity. Most battery types will have a much longer life if we never let them get below 50% DOD. Therefore, we need at least 600 ah of battery capacity. If we are at anchor and want to do some inland travel for a couple of days, it would be nice to have enough reserve capacity to ensure the refrigerator will keep running while we’re gone, so let’s assume we would like at least 800 ah of capacity.

wind gen

  • Recharging. We have solar panels and a wind generator, which combined, average about 80 ah each day, and a shaft generator that puts out quite a bit of power – typically another 60 ah a day when we’re sailing. So, let’s assume we have to replenish around 100 ah per day using the engine. We have a 200 amp alternator, but unless we are running the engine at max rpm, it generates far less amperage than this. We typically run the engine at about 1500 rpm while recharging, which produces around 110 amps. Our engine consumes about 1.4 gallons of fuel per hour at this speed. Fuel prices around the world vary – ranging from $0.12 a gallon in Venezuela to more than $12 a gallon in St. Helena. In the U.S., let’s use an average of $2.50 a gallon for marine diesel, so it costs about $3.50 per hour to recharge at 110 amps per hour.
  • Recharge cycles. We are sailing or on the hook about 75% of the time and are without shore power around 275 days each year. We don’t typically need to run the engine every day, so let’s assume we recharge the batteries from 50% DOD 200 days each year.

After all that preliminary stuff, it’s finally time to look at the battery choices. What I plan to do is to examine each type of battery chemistry, list the pros and cons of each, then evaluate the size, weight, number of batteries, purchase price and actual cost of each for our new battery battery bank.

Unfortunately, I’m going to have to put that off until next week’s Blue View – I’m still collecting data and specs from a few battery manufacturers. Stay tuned.

By the way, thanks to the several folks who commented or contacted me regarding battery information and ideas.