Does phosphoric acid improve cycle life in lead–acid batteries?

Phosphoric acid (sometimes confused with “fosferic acid”) has been used as an additive in lead–acid battery electrolytes, but not as a replacement for sulphuric acid.

When added in small amounts, phosphoric acid forms stable compounds on the positive plate that help reduce corrosion, shedding of active material, and sulphation. This effect can noticeably extend the cycle life of a battery, especially under deep-cycle use where the plates are stressed over many charge/discharge events.

The benefits:

  • Extended cycle life in renewable energy and stationary applications.
  • Reduced sulphation, which is one of the main failure modes of deep-cycle lead–acid batteries.
  • Improved adhesion of active material to the grid, reducing plate degradation.

The trade-offs:

  • Higher internal resistance reduces cranking performance and fast discharge capability, making it less suited for starter batteries.
  • Reduced charge acceptance compared to conventional sulphuric acid electrolyte.
  • Primarily beneficial in deep-cycle applications (telecom, UPS float, renewable storage), rather than automotive cranking or TPPL AGM designs like Odyssey.

Industry use

Some tubular flooded cells and stationary batteries have adopted phosphoric acid additives, but it’s less common in sealed AGM or Gel batteries. Those chemistries are already optimised for long life, and TPPL (Thin Plate Pure Lead) designs such as Odyssey focus on high cranking output rather than maximising cycle life.

In short: Yes, phosphoric acid can improve cycle life, but it does so at the expense of high-current performance. That’s why it’s sometimes used in deep-cycle stationary batteries, but not in starting or TPPL AGM batteries.

How many solar panels do I need?

This question is best answered by asking, how much do you use?

By building a load profile that outlines all the power you intend to consume during a day and estimating the duration of each device and its power draw you can build a power profile. A power bill is similar but not to the same level of detail as it only shows a total for the month which you divide by the number of days in that month. That gives you a kWh value. That number is sometimes referred to as the number of units. It's what you are charged for on your power bill. i.e. 500 units for the month at 20 cents per unit (1 kWh) would be $100. 500 units divided by 31 days equals 16.12 units per day. So that's 16kWh, and in New Zealand, the peak sun hours over winter are only 2 hours. So you'd need an 8kW solar array which will produce on a clear day 8kW per hour and with the 2 hours of usable sun energy in a day you'd generate 16kWh of power.

This would generate enough power to offset your consumption, but it's not all at the right time. You use power at night from the grid so you'll be charged for importing power to your house. But during the day while you aren't at home or your power usage is low you'll be exporting to the grid which may result in you receiving a small credit to your account.

You can see how the real way to benefit from solar is to utilise the sun's energy during the day and limit your need for it at night. This is where batteries can help as they store the day's energy for you to use at night.

Which is better Optima or Odyssey

The choice between Optima and Odyssey batteries depends on your specific needs and preferences, as both brands offer high-quality batteries with their own unique features and advantages.

Optima Batteries:

  • Optima batteries are known for their distinctive spiral-wound design or different coloured tops, Yellow, Red & Blue
  • They are designed to deliver a high burst of energy, making them suitable for starting applications and providing strong cranking power.
  • Optima batteries are also spill-proof and maintenance-free AGM design with pure lead.
  • These batteries are known for their reliability and are often used in performance and enthusiast vehicles and are lighter weight than the same sized Odyssey because of the lower capacity (Ah).

Odyssey Batteries:

  • Odyssey batteries are recognized for their robust deep cycle capabilities because of the increased Ah, making them suitable for applications that require continuous and deep discharging, such as RVs, boats, and solar systems.
  • They too are designed to deliver a high burst of energy, making them suitable for starting applications and providing strong cranking power because they are pure lead AGM.
  • Odyssey batteries are known for their long service life and strong performance in demanding conditions.
  • They are versatile and can be used for both starting and deep cycling applications.

The choice between Optima and Odyssey batteries depends on your specific needs. If you require a battery primarily for starting applications in vehicles and prefer a unique spiral-wound design, Optima batteries might be a good choice. On the other hand, if you need a battery that excels in deep cycling and can handle sustained discharging, Odyssey batteries are a strong option. Consider the requirements of your particular application and select the battery that aligns with those needs. Both brands are known for their quality, so you can't go wrong with either choice.

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