How Long Does A Marine Battery Hold Charge?

You’ve been saving up for this for a long time. It’s been your dream to go out over the water and just relax with the silent slapping of the water across the sides of the boat, the wind whistling by and some sun to make up for all the time you’ve been working indoors.

You go over the boats listed for sale and settle on one beauty. You check her out, she seems to be in good condition. The batteries that came with it are what could be a worry for you. Even though they’re fairly new, you have no idea how they’d been used before and so you wonder…

How long does marine battery hold charge? Well, that will depend on what the battery is being used for. A marine battery is no different from most of these other automotive batteries, they are just specialized for the needs of people operating boats. That means that they are subject to the same factors that will affect how long the battery will hold charge.

To better understand how long the battery will hold charge, it would be prudent to take a look into what these factors are and if you suspect that battery has been through some of them, what to do to prevent from getting stranded in the middle of a body of water.

1. How Long Has the Battery Been in Use

Some boat seller will also pass to you all the maintenance sheets that relate to the boat. The one that you should immediately look for are the battery receipts. These could be either the receipt of purchase, or battery maintenance reports.

The longer a battery has been in use, the more the plates inside it have experienced some wear and tear. This is normal during a chemical process but becomes more pronounced as the battery ages. If you take a look at the battery and see some brown sludge sloshing around at the bottom of the battery, this is one indicator that the battery has seen better days.

This is as a result of a process known as plate shedding. The battery is made up of an electrolyte and two plates. The negative plate is made of spongy lead-based product. The positive is made of powder like lead peroxide material.

Whenever the battery is discharging, some sulfates form inside the battery. These sulfates will then bind the powdery peroxide of the positive plate causing them to form lumps. When the battery is recharged, the sulfates then become active and cause the powder to lose some of its coherence. Bits will then drop off the positive plate and to the bottom of the battery.

In certain cases, the formation of gases inside the battery will cause this combined substance to fall off the plate, or a sloshing around of the acid as the boat rocks from side to side helps the acid wash the peroxide from the positive plate.

This is a completely normal process. However, the severity of the browning is an indicator of how long the battery has been in use, and should probably be replaced.

2. Temperature and Humidity

Back in Chemistry classes, the teachers would tell us that there are several things that affect the rate of a reaction. Among them is the concentration of the solution. Well, sulfuric acid is a pretty strong acid that is capable of melting metal but that’s not what you’re here for.

The other thing that affects the rate of reaction is temperature. The higher the temperature, the faster and more intensive the reaction will be. A marine battery is just a big chemical experiment that paid dividends and now powers all forms of automotive vehicles on earth.

In this case, the temperature will affect the integrity of the plates inside the battery. During cold temperatures, the positive plate is the one that will suffer degradation during charging. It will cause the peroxide plate to begin flaking and the powder dropping off the plate. The cold also increases resistance to flow of power, thus the battery will need to push more power to be able to overcome the resistance and power the boat.

Heat on the other hand has a direct hand in how long the marine battery will last. A 10 degree Celsius/50 degrees Fahrenheit rise in temperature will cause the battery to lose half its intended life. This is the reason why battery manufacturers like quoting the life of the battery at 20 degrees Celsius/68 degrees Fahrenheit.

3. Incorrect Charging

As mentioned earlier, a marine battery is one of the simplest chemical experiments that could have been put out for everyday use. The electrolyte and the plates in the battery are pretty sensitive and if they are not charged correctly, or charged beyond their capacity, this could result in damage to the battery.

Undercharging leads to a process known as sulfation. This is a normal process that occurs in the battery every time it is discharged. The electrolyte will give out sulfates, which will then travel to the negative plate and give up their charge. These chargeless sulfates will begin to bind with the negative plate. When the battery is recharged, the sulfates detach from their plate to take back their charge.

When the battery is undercharged, these sulfates build on the plate. If it continues, this sulfation will continue building and hardening, and therefore causing resistance to flow of power out of the battery. This will mean that the battery will have to push out more power to overcome the resistance and not last long.

This sulfation is also a by-product of poor maintenance techniques. A battery should be maintained by adding mineral free, or distilled water into it. If anything other than the two was introduced to it, say like tap water, this could introduce impurities into the battery
Overcharging on the other hand causes the electrolyte to break down and release hydrogen gas. This is a flammable gas and when it comes into contact with a spark will cause serious explosions and boat fires.

Sources:
1. How temperature affects batteries – Tawaki Battery